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 $58.99   11.692%   $65.8871   $65.89   $65.90   $65.90  
  Purchase #2 $237.72   12.725%   $267.9699   $267.97   $267.95   $268.00  
  Purchase #3 $17.73   11.406%   $19.7523   $19.75   $19.75   $19.80  
  Purchase #4 $188.70   12.598%   $212.4724   $212.47   $212.45   $212.50  
  Purchase #5 $116.27   5.674%   $122.8672   $122.87   $122.85   $122.90  
  Purchase #6 $204.82   9.852%   $224.9989   $225.00   $225.00   $225.00  
  Purchase #7 $123.51   10.776%   $136.8194   $136.82   $136.80   $136.80  
  7 purchase totals = $947.74       $1,050.7672   $1,050.77   $1,050.70   $1,050.90