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 $92.35   10.103%   $101.6801   $101.68   $101.70   $101.70  
  Purchase #2 $140.37   11.155%   $156.0283   $156.03   $156.05   $156.00  
  Purchase #3 $108.30   7.375%   $116.2871   $116.29   $116.30   $116.30  
  Purchase #4 $250.90   7.423%   $269.5243   $269.52   $269.50   $269.50  
  Purchase #5 $125.60   10.239%   $138.4602   $138.46   $138.45   $138.50  
  Purchase #6 $91.35   3.248%   $94.317   $94.32   $94.30   $94.30  
  Purchase #7 $149.39   12.187%   $167.5962   $167.60   $167.60   $167.60  
  7 purchase totals = $958.26       $1,043.8932   $1,043.90   $1,043.90   $1,043.90