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 $53.90   10.750%   $59.6943   $59.69   $59.70   $59.70  
  Purchase #2 $117.62   9.138%   $128.3681   $128.37   $128.35   $128.40  
  Purchase #3 $215.42   9.645%   $236.1973   $236.20   $236.20   $236.20  
  Purchase #4 $21.66   5.627%   $22.8788   $22.88   $22.90   $22.90  
  Purchase #5 $226.43   3.623%   $234.6336   $234.63   $234.65   $234.60  
  Purchase #6 $182.25   5.617%   $192.487   $192.49   $192.50   $192.50  
  Purchase #7 $97.98   11.704%   $109.4476   $109.45   $109.45   $109.40  
  7 purchase totals = $915.26       $983.7067   $983.71   $983.75   $983.70