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 $54.38   8.488%   $58.9958   $59.00   $59.00   $59.00  
  Purchase #2 $10.41   3.406%   $10.7646   $10.76   $10.75   $10.80  
  Purchase #3 $97.58   7.225%   $104.6302   $104.63   $104.65   $104.60  
  Purchase #4 $102.86   8.828%   $111.9405   $111.94   $111.95   $111.90  
  Purchase #5 $235.99   4.446%   $246.4821   $246.48   $246.50   $246.50  
  Purchase #6 $63.25   11.125%   $70.2866   $70.29   $70.30   $70.30  
  Purchase #7 $99.26   5.630%   $104.8483   $104.85   $104.85   $104.80  
  7 purchase totals = $663.73       $707.9481   $707.95   $708.00   $707.90