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 $119.64   10.772%   $132.5276   $132.53   $132.55   $132.50  
  Purchase #2 $109.69   10.649%   $121.3709   $121.37   $121.35   $121.40  
  Purchase #3 $204.96   10.484%   $226.448   $226.45   $226.45   $226.40  
  Purchase #4 $211.48   10.737%   $234.1866   $234.19   $234.20   $234.20  
  Purchase #5 $28.79   10.132%   $31.707   $31.71   $31.70   $31.70  
  Purchase #6 $31.33   9.719%   $34.375   $34.38   $34.40   $34.40  
  Purchase #7 $59.39   7.556%   $63.8775   $63.88   $63.90   $63.90  
  7 purchase totals = $765.28       $844.4926   $844.51   $844.55   $844.50