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 $85.72   12.459%   $96.3999   $96.40   $96.40   $96.40  
  Purchase #2 $236.96   12.843%   $267.3928   $267.39   $267.40   $267.40  
  Purchase #3 $129.72   3.252%   $133.9385   $133.94   $133.95   $133.90  
  Purchase #4 $160.76   12.246%   $180.4467   $180.45   $180.45   $180.40  
  Purchase #5 $143.77   6.719%   $153.4299   $153.43   $153.45   $153.40  
  Purchase #6 $152.38   13.626%   $173.1433   $173.14   $173.15   $173.10  
  Purchase #7 $246.65   8.484%   $267.5758   $267.58   $267.60   $267.60  
  7 purchase totals = $1,155.96       $1,272.3269   $1,272.33   $1,272.40   $1,272.20