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 $114.84   8.299%   $124.3706   $124.37   $124.35   $124.40  
  Purchase #2 $181.87   10.110%   $200.2571   $200.26   $200.25   $200.30  
  Purchase #3 $52.85   4.126%   $55.0306   $55.03   $55.05   $55.00  
  Purchase #4 $217.52   8.650%   $236.3355   $236.34   $236.35   $236.30  
  Purchase #5 $143.85   10.508%   $158.9658   $158.97   $158.95   $159.00  
  Purchase #6 $202.40   10.583%   $223.82   $223.82   $223.80   $223.80  
  Purchase #7 $121.70   4.763%   $127.4966   $127.50   $127.50   $127.50  
  7 purchase totals = $1,035.03       $1,126.2762   $1,126.29   $1,126.25   $1,126.30