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 $42.33   12.407%   $47.5819   $47.58   $47.60   $47.60  
  Purchase #2 $186.28   7.702%   $200.6273   $200.63   $200.65   $200.60  
  Purchase #3 $159.34   9.365%   $174.2622   $174.26   $174.25   $174.30  
  Purchase #4 $40.98   12.515%   $46.1086   $46.11   $46.10   $46.10  
  Purchase #5 $135.50   13.267%   $153.4768   $153.48   $153.50   $153.50  
  Purchase #6 $235.57   3.860%   $244.663   $244.66   $244.65   $244.70  
  Purchase #7 $108.71   4.433%   $113.5291   $113.53   $113.55   $113.50  
  7 purchase totals = $908.71       $980.2489   $980.25   $980.30   $980.30