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 $44.89   8.255%   $48.5957   $48.60   $48.60   $48.60  
  Purchase #2 $65.50   10.242%   $72.2085   $72.21   $72.20   $72.20  
  Purchase #3 $214.69   10.322%   $236.8503   $236.85   $236.85   $236.90  
  Purchase #4 $69.67   11.264%   $77.5176   $77.52   $77.50   $77.50  
  Purchase #5 $195.90   6.107%   $207.8636   $207.86   $207.85   $207.90  
  Purchase #6 $129.61   12.219%   $145.447   $145.45   $145.45   $145.40  
  Purchase #7 $193.78   4.341%   $202.192   $202.19   $202.20   $202.20  
  7 purchase totals = $914.04       $990.6747   $990.68   $990.65   $990.70