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 $52.93   12.199%   $59.3869   $59.39   $59.40   $59.40  
  Purchase #2 $248.98   10.819%   $275.9171   $275.92   $275.90   $275.90  
  Purchase #3 $195.25   8.324%   $211.5026   $211.50   $211.50   $211.50  
  Purchase #4 $213.43   10.426%   $235.6822   $235.68   $235.70   $235.70  
  Purchase #5 $213.84   12.371%   $240.2941   $240.29   $240.30   $240.30  
  Purchase #6 $140.99   4.766%   $147.7096   $147.71   $147.70   $147.70  
  Purchase #7 $213.72   5.365%   $225.1861   $225.19   $225.20   $225.20  
  7 purchase totals = $1,279.14       $1,395.6786   $1,395.68   $1,395.70   $1,395.70