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 $244.92   12.534%   $275.6183   $275.62   $275.60   $275.60  
  Purchase #2 $222.65   6.822%   $237.8392   $237.84   $237.85   $237.80  
  Purchase #3 $171.76   12.468%   $193.175   $193.18   $193.20   $193.20  
  Purchase #4 $152.88   8.730%   $166.2264   $166.23   $166.25   $166.20  
  Purchase #5 $58.89   12.473%   $66.2353   $66.24   $66.25   $66.20  
  Purchase #6 $61.72   5.345%   $65.0189   $65.02   $65.00   $65.00  
  Purchase #7 $167.63   5.352%   $176.6016   $176.60   $176.60   $176.60  
  7 purchase totals = $1,080.45       $1,180.7147   $1,180.73   $1,180.75   $1,180.60