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 $81.51   12.822%   $91.9612   $91.96   $91.95   $92.00  
  Purchase #2 $55.73   5.274%   $58.6692   $58.67   $58.65   $58.70  
  Purchase #3 $27.36   8.467%   $29.6766   $29.68   $29.70   $29.70  
  Purchase #4 $65.49   11.532%   $73.0423   $73.04   $73.05   $73.00  
  Purchase #5 $160.93   10.575%   $177.9483   $177.95   $177.95   $177.90  
  Purchase #6 $178.27   12.707%   $200.9228   $200.92   $200.90   $200.90  
  Purchase #7 $41.54   13.761%   $47.2563   $47.26   $47.25   $47.30  
  7 purchase totals = $610.83       $679.4767   $679.48   $679.45   $679.50