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 $169.86   6.571%   $181.0215   $181.02   $181.00   $181.00  
  Purchase #2 $209.57   4.762%   $219.5497   $219.55   $219.55   $219.50  
  Purchase #3 $144.36   3.244%   $149.043   $149.04   $149.05   $149.00  
  Purchase #4 $124.31   7.382%   $133.4866   $133.49   $133.50   $133.50  
  Purchase #5 $141.55   11.826%   $158.2897   $158.29   $158.30   $158.30  
  Purchase #6 $199.56   12.725%   $224.954   $224.95   $224.95   $225.00  
  Purchase #7 $126.94   7.717%   $136.736   $136.74   $136.75   $136.70  
  7 purchase totals = $1,116.15       $1,203.0805   $1,203.08   $1,203.10   $1,203.00