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 $94.96   6.626%   $101.252   $101.25   $101.25   $101.30  
  Purchase #2 $151.50   6.832%   $161.8505   $161.85   $161.85   $161.90  
  Purchase #3 $116.73   7.475%   $125.4556   $125.46   $125.45   $125.50  
  Purchase #4 $195.41   6.616%   $208.3383   $208.34   $208.35   $208.30  
  Purchase #5 $150.28   12.426%   $168.9538   $168.95   $168.95   $169.00  
  Purchase #6 $111.94   13.279%   $126.8045   $126.80   $126.80   $126.80  
  Purchase #7 $25.46   7.868%   $27.4632   $27.46   $27.45   $27.50  
  7 purchase totals = $846.28       $920.1179   $920.11   $920.10   $920.30