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 $210.85   10.378%   $232.732   $232.73   $232.75   $232.70  
  Purchase #2 $141.65   6.395%   $150.7085   $150.71   $150.70   $150.70  
  Purchase #3 $134.87   12.663%   $151.9486   $151.95   $151.95   $151.90  
  Purchase #4 $214.33   10.865%   $237.617   $237.62   $237.60   $237.60  
  Purchase #5 $169.86   6.129%   $180.2707   $180.27   $180.25   $180.30  
  Purchase #6 $149.61   12.324%   $168.0479   $168.05   $168.05   $168.00  
  Purchase #7 $42.48   13.470%   $48.2021   $48.20   $48.20   $48.20  
  7 purchase totals = $1,063.65       $1,169.5268   $1,169.53   $1,169.50   $1,169.40