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 $40.95   13.157%   $46.3378   $46.34   $46.35   $46.30  
  Purchase #2 $146.53   12.270%   $164.5092   $164.51   $164.50   $164.50  
  Purchase #3 $158.51   4.229%   $165.2134   $165.21   $165.20   $165.20  
  Purchase #4 $24.25   9.836%   $26.6352   $26.64   $26.65   $26.60  
  Purchase #5 $246.89   5.585%   $260.6788   $260.68   $260.70   $260.70  
  Purchase #6 $107.67   9.459%   $117.8545   $117.85   $117.85   $117.90  
  Purchase #7 $163.89   8.227%   $177.3732   $177.37   $177.35   $177.40  
  7 purchase totals = $888.69       $958.6021   $958.60   $958.60   $958.60