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 $190.83   6.633%   $203.4878   $203.49   $203.50   $203.50  
  Purchase #2 $77.38   8.121%   $83.664   $83.66   $83.65   $83.70  
  Purchase #3 $228.86   3.237%   $236.2682   $236.27   $236.25   $236.30  
  Purchase #4 $148.63   6.773%   $158.6967   $158.70   $158.70   $158.70  
  Purchase #5 $65.40   13.212%   $74.0406   $74.04   $74.05   $74.00  
  Purchase #6 $225.31   3.200%   $232.5199   $232.52   $232.50   $232.50  
  Purchase #7 $55.62   5.176%   $58.4989   $58.50   $58.50   $58.50  
  7 purchase totals = $992.03       $1,047.1761   $1,047.18   $1,047.15   $1,047.20