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 $41.59   6.533%   $44.3071   $44.31   $44.30   $44.30  
  Purchase #2 $148.90   11.356%   $165.8091   $165.81   $165.80   $165.80  
  Purchase #3 $85.92   12.465%   $96.6299   $96.63   $96.65   $96.60  
  Purchase #4 $50.77   9.314%   $55.4987   $55.50   $55.50   $55.50  
  Purchase #5 $231.54   4.609%   $242.2117   $242.21   $242.20   $242.20  
  Purchase #6 $81.88   11.664%   $91.4305   $91.43   $91.45   $91.40  
  Purchase #7 $66.74   4.110%   $69.483   $69.48   $69.50   $69.50  
  7 purchase totals = $707.34       $765.3700   $765.37   $765.40   $765.30