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 $62.27   7.143%   $66.7179   $66.72   $66.70   $66.70  
  Purchase #2 $240.98   6.873%   $257.5426   $257.54   $257.55   $257.50  
  Purchase #3 $84.82   10.486%   $93.7142   $93.71   $93.70   $93.70  
  Purchase #4 $171.55   8.624%   $186.3445   $186.34   $186.35   $186.30  
  Purchase #5 $82.82   8.314%   $89.7057   $89.71   $89.70   $89.70  
  Purchase #6 $236.91   9.741%   $259.9874   $259.99   $260.00   $260.00  
  Purchase #7 $142.64   9.725%   $156.5117   $156.51   $156.50   $156.50  
  7 purchase totals = $1,021.99       $1,110.5240   $1,110.52   $1,110.50   $1,110.40