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 $210.56   12.361%   $236.5873   $236.59   $236.60   $236.60  
  Purchase #2 $246.96   5.329%   $260.1205   $260.12   $260.10   $260.10  
  Purchase #3 $23.85   11.236%   $26.5298   $26.53   $26.55   $26.50  
  Purchase #4 $67.70   12.488%   $76.1544   $76.15   $76.15   $76.20  
  Purchase #5 $33.76   9.623%   $37.0087   $37.01   $37.00   $37.00  
  Purchase #6 $181.92   4.790%   $190.634   $190.63   $190.65   $190.60  
  Purchase #7 $5.87   5.282%   $6.1801   $6.18   $6.20   $6.20  
  7 purchase totals = $770.62       $833.2148   $833.21   $833.25   $833.20