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 $64.38   7.251%   $69.0482   $69.05   $69.05   $69.00  
  Purchase #2 $77.36   6.332%   $82.2584   $82.26   $82.25   $82.30  
  Purchase #3 $151.58   3.166%   $156.379   $156.38   $156.40   $156.40  
  Purchase #4 $49.30   3.647%   $51.098   $51.10   $51.10   $51.10  
  Purchase #5 $219.63   12.817%   $247.78   $247.78   $247.80   $247.80  
  Purchase #6 $129.25   10.359%   $142.639   $142.64   $142.65   $142.60  
  Purchase #7 $12.80   7.827%   $13.8019   $13.80   $13.80   $13.80  
  7 purchase totals = $704.30       $763.0045   $763.01   $763.05   $763.00