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 $130.93   13.236%   $148.2599   $148.26   $148.25   $148.30  
  Purchase #2 $224.72   11.297%   $250.1066   $250.11   $250.10   $250.10  
  Purchase #3 $168.38   10.668%   $186.3428   $186.34   $186.35   $186.30  
  Purchase #4 $179.26   8.518%   $194.5294   $194.53   $194.55   $194.50  
  Purchase #5 $243.88   12.136%   $273.4773   $273.48   $273.50   $273.50  
  Purchase #6 $149.59   5.339%   $157.5766   $157.58   $157.60   $157.60  
  Purchase #7 $51.61   13.390%   $58.5206   $58.52   $58.50   $58.50  
  7 purchase totals = $1,148.37       $1,268.8132   $1,268.82   $1,268.85   $1,268.80