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 $24.77   6.281%   $26.3258   $26.33   $26.35   $26.30  
  Purchase #2 $104.69   6.362%   $111.3504   $111.35   $111.35   $111.40  
  Purchase #3 $41.87   8.305%   $45.3473   $45.35   $45.35   $45.30  
  Purchase #4 $120.60   13.868%   $137.3248   $137.32   $137.30   $137.30  
  Purchase #5 $178.68   13.174%   $202.2193   $202.22   $202.20   $202.20  
  Purchase #6 $169.80   8.639%   $184.469   $184.47   $184.45   $184.50  
  Purchase #7 $68.35   12.555%   $76.9313   $76.93   $76.95   $76.90  
  7 purchase totals = $708.76       $783.9679   $783.97   $783.95   $783.90