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 $32.41   6.653%   $34.5662   $34.57   $34.55   $34.60  
  Purchase #2 $119.36   3.386%   $123.4015   $123.40   $123.40   $123.40  
  Purchase #3 $42.25   12.438%   $47.5051   $47.51   $47.50   $47.50  
  Purchase #4 $53.61   9.692%   $58.8059   $58.81   $58.80   $58.80  
  Purchase #5 $225.52   8.212%   $244.0397   $244.04   $244.05   $244.00  
  Purchase #6 $22.48   11.742%   $25.1196   $25.12   $25.10   $25.10  
  Purchase #7 $99.27   9.299%   $108.5011   $108.50   $108.50   $108.50  
  7 purchase totals = $594.90       $641.9391   $641.95   $641.90   $641.90