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 $212.43   11.361%   $236.5642   $236.56   $236.55   $236.60  
  Purchase #2 $80.60   13.480%   $91.4649   $91.46   $91.45   $91.50  
  Purchase #3 $214.87   8.241%   $232.5774   $232.58   $232.60   $232.60  
  Purchase #4 $248.67   5.323%   $261.9067   $261.91   $261.90   $261.90  
  Purchase #5 $105.80   13.165%   $119.7286   $119.73   $119.75   $119.70  
  Purchase #6 $46.56   11.747%   $52.0294   $52.03   $52.05   $52.00  
  Purchase #7 $37.96   5.549%   $40.0664   $40.07   $40.05   $40.10  
  7 purchase totals = $946.89       $1,034.3376   $1,034.34   $1,034.35   $1,034.40