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 $231.41   11.573%   $258.1911   $258.19   $258.20   $258.20  
  Purchase #2 $163.57   11.511%   $182.3985   $182.40   $182.40   $182.40  
  Purchase #3 $51.98   5.350%   $54.7609   $54.76   $54.75   $54.80  
  Purchase #4 $16.60   3.571%   $17.1928   $17.19   $17.20   $17.20  
  Purchase #5 $198.53   7.624%   $213.6659   $213.67   $213.65   $213.70  
  Purchase #6 $88.83   6.127%   $94.2726   $94.27   $94.25   $94.30  
  Purchase #7 $128.67   7.572%   $138.4129   $138.41   $138.40   $138.40  
  7 purchase totals = $879.59       $958.8947   $958.89   $958.85   $959.00