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 $167.74   13.838%   $190.9519   $190.95   $190.95   $191.00  
  Purchase #2 $19.44   9.359%   $21.2594   $21.26   $21.25   $21.30  
  Purchase #3 $126.62   6.162%   $134.4223   $134.42   $134.40   $134.40  
  Purchase #4 $178.79   12.794%   $201.6644   $201.66   $201.65   $201.70  
  Purchase #5 $182.93   10.363%   $201.887   $201.89   $201.90   $201.90  
  Purchase #6 $182.27   5.686%   $192.6339   $192.63   $192.65   $192.60  
  Purchase #7 $41.53   9.271%   $45.3802   $45.38   $45.40   $45.40  
  7 purchase totals = $899.32       $988.1991   $988.19   $988.20   $988.30