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 $60.95   6.683%   $65.0233   $65.02   $65.00   $65.00  
  Purchase #2 $50.52   3.196%   $52.1346   $52.13   $52.15   $52.10  
  Purchase #3 $236.52   4.548%   $247.2769   $247.28   $247.30   $247.30  
  Purchase #4 $87.33   12.778%   $98.489   $98.49   $98.50   $98.50  
  Purchase #5 $174.60   12.843%   $197.0239   $197.02   $197.00   $197.00  
  Purchase #6 $209.93   13.157%   $237.5505   $237.55   $237.55   $237.60  
  Purchase #7 $103.98   9.532%   $113.8914   $113.89   $113.90   $113.90  
  7 purchase totals = $923.83       $1,011.3896   $1,011.38   $1,011.40   $1,011.40