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 $82.60   12.541%   $92.9589   $92.96   $92.95   $93.00  
  Purchase #2 $73.87   3.364%   $76.355   $76.36   $76.35   $76.40  
  Purchase #3 $35.25   7.607%   $37.9315   $37.93   $37.95   $37.90  
  Purchase #4 $142.42   11.201%   $158.3725   $158.37   $158.35   $158.40  
  Purchase #5 $185.45   7.519%   $199.394   $199.39   $199.40   $199.40  
  Purchase #6 $97.74   12.794%   $110.2449   $110.24   $110.25   $110.20  
  Purchase #7 $200.55   5.605%   $211.7908   $211.79   $211.80   $211.80  
  7 purchase totals = $817.88       $887.0476   $887.04   $887.05   $887.10