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 $219.84   9.669%   $241.0963   $241.10   $241.10   $241.10  
  Purchase #2 $180.91   12.615%   $203.7318   $203.73   $203.75   $203.70  
  Purchase #3 $44.90   10.248%   $49.5014   $49.50   $49.50   $49.50  
  Purchase #4 $57.89   10.237%   $63.8162   $63.82   $63.80   $63.80  
  Purchase #5 $46.72   11.119%   $51.9148   $51.91   $51.90   $51.90  
  Purchase #6 $82.48   8.419%   $89.424   $89.42   $89.40   $89.40  
  Purchase #7 $88.25   6.768%   $94.2228   $94.22   $94.20   $94.20  
  7 purchase totals = $720.99       $793.7073   $793.70   $793.65   $793.60