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 $83.96   5.676%   $88.7256   $88.73   $88.75   $88.70  
  Purchase #2 $181.89   12.279%   $204.2243   $204.22   $204.20   $204.20  
  Purchase #3 $190.89   11.787%   $213.3902   $213.39   $213.40   $213.40  
  Purchase #4 $54.66   13.831%   $62.22   $62.22   $62.20   $62.20  
  Purchase #5 $200.67   4.632%   $209.965   $209.97   $209.95   $210.00  
  Purchase #6 $128.73   7.218%   $138.0217   $138.02   $138.00   $138.00  
  Purchase #7 $205.74   9.136%   $224.5364   $224.54   $224.55   $224.50  
  7 purchase totals = $1,046.54       $1,141.0832   $1,141.09   $1,141.05   $1,141.00