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 $114.91   10.246%   $126.6837   $126.68   $126.70   $126.70  
  Purchase #2 $206.75   7.776%   $222.8269   $222.83   $222.85   $222.80  
  Purchase #3 $62.50   7.159%   $66.9744   $66.97   $66.95   $67.00  
  Purchase #4 $178.88   10.440%   $197.5551   $197.56   $197.55   $197.60  
  Purchase #5 $216.96   5.265%   $228.3829   $228.38   $228.40   $228.40  
  Purchase #6 $25.32   13.816%   $28.8182   $28.82   $28.80   $28.80  
  Purchase #7 $157.91   3.795%   $163.9027   $163.90   $163.90   $163.90  
  7 purchase totals = $963.23       $1,035.1439   $1,035.14   $1,035.15   $1,035.20