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 $227.47   5.485%   $239.9467   $239.95   $239.95   $239.90  
  Purchase #2 $49.35   12.615%   $55.5755   $55.58   $55.60   $55.60  
  Purchase #3 $47.84   7.609%   $51.4801   $51.48   $51.50   $51.50  
  Purchase #4 $150.59   10.446%   $166.3206   $166.32   $166.30   $166.30  
  Purchase #5 $12.49   11.386%   $13.9121   $13.91   $13.90   $13.90  
  Purchase #6 $152.41   12.618%   $171.6411   $171.64   $171.65   $171.60  
  Purchase #7 $60.77   4.264%   $63.3612   $63.36   $63.35   $63.40  
  7 purchase totals = $700.92       $762.2373   $762.24   $762.25   $762.20