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 $42.85   13.231%   $48.5195   $48.52   $48.50   $48.50  
  Purchase #2 $193.33   7.791%   $208.3923   $208.39   $208.40   $208.40  
  Purchase #3 $93.32   11.123%   $103.7   $103.70   $103.70   $103.70  
  Purchase #4 $119.80   8.577%   $130.0752   $130.08   $130.10   $130.10  
  Purchase #5 $51.79   5.193%   $54.4795   $54.48   $54.50   $54.50  
  Purchase #6 $239.62   11.843%   $267.9982   $268.00   $268.00   $268.00  
  Purchase #7 $178.98   10.150%   $197.1465   $197.15   $197.15   $197.10  
  7 purchase totals = $919.69       $1,010.3112   $1,010.32   $1,010.35   $1,010.30