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 $59.37   11.356%   $66.1121   $66.11   $66.10   $66.10  
  Purchase #2 $188.87   7.231%   $202.5272   $202.53   $202.55   $202.50  
  Purchase #3 $158.78   3.317%   $164.0467   $164.05   $164.05   $164.00  
  Purchase #4 $5.62   11.352%   $6.258   $6.26   $6.25   $6.30  
  Purchase #5 $156.86   8.644%   $170.419   $170.42   $170.40   $170.40  
  Purchase #6 $237.58   3.331%   $245.4938   $245.49   $245.50   $245.50  
  Purchase #7 $176.81   6.115%   $187.6219   $187.62   $187.60   $187.60  
  7 purchase totals = $983.89       $1,042.4787   $1,042.48   $1,042.45   $1,042.40