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 $207.32   9.646%   $227.3181   $227.32   $227.30   $227.30  
  Purchase #2 $166.87   10.692%   $184.7117   $184.71   $184.70   $184.70  
  Purchase #3 $66.27   3.316%   $68.4675   $68.47   $68.45   $68.50  
  Purchase #4 $141.39   11.419%   $157.5353   $157.54   $157.55   $157.50  
  Purchase #5 $213.81   8.800%   $232.6253   $232.63   $232.65   $232.60  
  Purchase #6 $216.62   9.624%   $237.4675   $237.47   $237.45   $237.50  
  Purchase #7 $146.84   6.116%   $155.8207   $155.82   $155.80   $155.80  
  7 purchase totals = $1,159.12       $1,263.9461   $1,263.96   $1,263.90   $1,263.90