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 $224.82   12.684%   $253.3362   $253.34   $253.35   $253.30  
  Purchase #2 $199.57   8.352%   $216.2381   $216.24   $216.25   $216.20  
  Purchase #3 $61.55   10.189%   $67.8213   $67.82   $67.80   $67.80  
  Purchase #4 $203.35   10.836%   $225.385   $225.39   $225.40   $225.40  
  Purchase #5 $215.60   7.125%   $230.9615   $230.96   $230.95   $231.00  
  Purchase #6 $97.25   5.781%   $102.872   $102.87   $102.85   $102.90  
  Purchase #7 $96.28   11.365%   $107.2222   $107.22   $107.20   $107.20  
  7 purchase totals = $1,098.42       $1,203.8363   $1,203.84   $1,203.80   $1,203.80