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 $17.78   8.182%   $19.2348   $19.23   $19.25   $19.20  
  Purchase #2 $166.56   9.390%   $182.2   $182.20   $182.20   $182.20  
  Purchase #3 $57.92   8.425%   $62.7998   $62.80   $62.80   $62.80  
  Purchase #4 $116.85   9.279%   $127.6925   $127.69   $127.70   $127.70  
  Purchase #5 $108.40   10.242%   $119.5023   $119.50   $119.50   $119.50  
  Purchase #6 $187.89   8.564%   $203.9809   $203.98   $204.00   $204.00  
  Purchase #7 $199.43   5.280%   $209.9599   $209.96   $209.95   $210.00  
  7 purchase totals = $854.83       $925.3702   $925.36   $925.40   $925.40