Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.87   7.685%   $253.9966   $254.00   $254.00   $254.00  
  Purchase #2 $160.40   4.593%   $167.7672   $167.77   $167.75   $167.80  
  Purchase #3 $151.83   4.654%   $158.8962   $158.90   $158.90   $158.90  
  Purchase #4 $186.35   13.209%   $210.965   $210.97   $210.95   $211.00  
  Purchase #5 $97.77   12.522%   $110.0128   $110.01   $110.00   $110.00  
  Purchase #6 $106.28   10.108%   $117.0228   $117.02   $117.00   $117.00  
  Purchase #7 $195.85   11.194%   $217.7734   $217.77   $217.75   $217.80  
  7 purchase totals = $1,134.35       $1,236.4340   $1,236.44   $1,236.35   $1,236.50