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 $45.54   13.620%   $51.7425   $51.74   $51.75   $51.70  
  Purchase #2 $23.32   13.440%   $26.4542   $26.45   $26.45   $26.50  
  Purchase #3 $224.82   12.208%   $252.266   $252.27   $252.25   $252.30  
  Purchase #4 $114.29   12.679%   $128.7808   $128.78   $128.80   $128.80  
  Purchase #5 $71.71   5.733%   $75.8211   $75.82   $75.80   $75.80  
  Purchase #6 $239.26   8.798%   $260.3101   $260.31   $260.30   $260.30  
  Purchase #7 $206.29   6.458%   $219.6122   $219.61   $219.60   $219.60  
  7 purchase totals = $925.23       $1,014.9869   $1,014.98   $1,014.95   $1,015.00