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 $104.81   3.311%   $108.2803   $108.28   $108.30   $108.30  
  Purchase #2 $62.41   4.628%   $65.2983   $65.30   $65.30   $65.30  
  Purchase #3 $232.35   5.734%   $245.6729   $245.67   $245.65   $245.70  
  Purchase #4 $121.58   4.764%   $127.3721   $127.37   $127.35   $127.40  
  Purchase #5 $126.89   5.136%   $133.4071   $133.41   $133.40   $133.40  
  Purchase #6 $22.60   8.822%   $24.5938   $24.59   $24.60   $24.60  
  Purchase #7 $214.33   10.401%   $236.6225   $236.62   $236.60   $236.60  
  7 purchase totals = $884.97       $941.2470   $941.24   $941.20   $941.30