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 $65.82   10.167%   $72.5119   $72.51   $72.50   $72.50  
  Purchase #2 $250.75   7.215%   $268.8416   $268.84   $268.85   $268.80  
  Purchase #3 $153.46   6.837%   $163.9521   $163.95   $163.95   $164.00  
  Purchase #4 $58.54   8.216%   $63.3496   $63.35   $63.35   $63.30  
  Purchase #5 $180.57   3.412%   $186.731   $186.73   $186.75   $186.70  
  Purchase #6 $141.96   3.348%   $146.7128   $146.71   $146.70   $146.70  
  Purchase #7 $38.50   3.795%   $39.9611   $39.96   $39.95   $40.00  
  7 purchase totals = $889.60       $942.0601   $942.05   $942.05   $942.00