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 $184.76   5.226%   $194.4156   $194.42   $194.40   $194.40  
  Purchase #2 $237.86   7.613%   $255.9683   $255.97   $255.95   $256.00  
  Purchase #3 $153.70   11.226%   $170.9544   $170.95   $170.95   $171.00  
  Purchase #4 $152.63   6.719%   $162.8852   $162.89   $162.90   $162.90  
  Purchase #5 $50.94   11.737%   $56.9188   $56.92   $56.90   $56.90  
  Purchase #6 $205.25   13.507%   $232.9731   $232.97   $232.95   $233.00  
  Purchase #7 $44.93   5.571%   $47.4331   $47.43   $47.45   $47.40  
  7 purchase totals = $1,030.07       $1,121.5485   $1,121.55   $1,121.50   $1,121.60