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 $133.59   11.128%   $148.4559   $148.46   $148.45   $148.50  
  Purchase #2 $198.65   13.625%   $225.7161   $225.72   $225.70   $225.70  
  Purchase #3 $194.93   6.780%   $208.1463   $208.15   $208.15   $208.10  
  Purchase #4 $233.61   4.811%   $244.849   $244.85   $244.85   $244.80  
  Purchase #5 $78.66   10.629%   $87.0208   $87.02   $87.00   $87.00  
  Purchase #6 $129.50   7.644%   $139.399   $139.40   $139.40   $139.40  
  Purchase #7 $143.97   5.145%   $151.3773   $151.38   $151.40   $151.40  
  7 purchase totals = $1,112.91       $1,204.9644   $1,204.98   $1,204.95   $1,204.90