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 $52.55   13.158%   $59.4645   $59.46   $59.45   $59.50  
  Purchase #2 $182.53   11.557%   $203.625   $203.63   $203.65   $203.60  
  Purchase #3 $202.36   8.141%   $218.8341   $218.83   $218.85   $218.80  
  Purchase #4 $164.74   11.517%   $183.7131   $183.71   $183.70   $183.70  
  Purchase #5 $55.63   11.155%   $61.8355   $61.84   $61.85   $61.80  
  Purchase #6 $238.47   11.465%   $265.8106   $265.81   $265.80   $265.80  
  Purchase #7 $231.79   12.257%   $260.2005   $260.20   $260.20   $260.20  
  7 purchase totals = $1,128.07       $1,253.4833   $1,253.48   $1,253.50   $1,253.40