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 $94.26   4.179%   $98.1991   $98.20   $98.20   $98.20  
  Purchase #2 $246.27   12.141%   $276.1696   $276.17   $276.15   $276.20  
  Purchase #3 $191.69   5.634%   $202.4898   $202.49   $202.50   $202.50  
  Purchase #4 $102.38   10.537%   $113.1678   $113.17   $113.15   $113.20  
  Purchase #5 $119.36   6.387%   $126.9835   $126.98   $127.00   $127.00  
  Purchase #6 $66.93   13.242%   $75.7929   $75.79   $75.80   $75.80  
  Purchase #7 $212.50   8.145%   $229.8081   $229.81   $229.80   $229.80  
  7 purchase totals = $1,033.39       $1,122.6108   $1,122.61   $1,122.60   $1,122.70