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 $119.73   5.669%   $126.5175   $126.52   $126.50   $126.50  
  Purchase #2 $57.30   3.765%   $59.4573   $59.46   $59.45   $59.50  
  Purchase #3 $163.79   3.277%   $169.1574   $169.16   $169.15   $169.20  
  Purchase #4 $205.39   13.196%   $232.4933   $232.49   $232.50   $232.50  
  Purchase #5 $63.69   4.849%   $66.7783   $66.78   $66.80   $66.80  
  Purchase #6 $135.69   3.568%   $140.5314   $140.53   $140.55   $140.50  
  Purchase #7 $221.50   6.856%   $236.686   $236.69   $236.70   $236.70  
  7 purchase totals = $967.09       $1,031.6212   $1,031.63   $1,031.65   $1,031.70