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 $201.52   6.699%   $215.0198   $215.02   $215.00   $215.00  
  Purchase #2 $104.94   13.438%   $119.0418   $119.04   $119.05   $119.00  
  Purchase #3 $68.28   10.800%   $75.6542   $75.65   $75.65   $75.70  
  Purchase #4 $132.70   3.593%   $137.4679   $137.47   $137.45   $137.50  
  Purchase #5 $125.53   7.759%   $135.2699   $135.27   $135.25   $135.30  
  Purchase #6 $162.68   11.170%   $180.8514   $180.85   $180.85   $180.90  
  Purchase #7 $133.67   6.469%   $142.3171   $142.32   $142.30   $142.30  
  7 purchase totals = $929.32       $1,005.6221   $1,005.62   $1,005.55   $1,005.70