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 $69.75   10.687%   $77.2042   $77.20   $77.20   $77.20  
  Purchase #2 $238.68   11.591%   $266.3454   $266.35   $266.35   $266.30  
  Purchase #3 $79.37   7.341%   $85.1966   $85.20   $85.20   $85.20  
  Purchase #4 $241.61   11.853%   $270.248   $270.25   $270.25   $270.20  
  Purchase #5 $206.65   10.166%   $227.658   $227.66   $227.65   $227.70  
  Purchase #6 $120.34   8.657%   $130.7578   $130.76   $130.75   $130.80  
  Purchase #7 $169.91   5.182%   $178.7147   $178.71   $178.70   $178.70  
  7 purchase totals = $1,126.31       $1,236.1247   $1,236.13   $1,236.10   $1,236.10