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 $68.46   13.287%   $77.5563   $77.56   $77.55   $77.60  
  Purchase #2 $46.79   10.711%   $51.8017   $51.80   $51.80   $51.80  
  Purchase #3 $54.71   11.305%   $60.895   $60.90   $60.90   $60.90  
  Purchase #4 $194.74   13.668%   $221.3571   $221.36   $221.35   $221.40  
  Purchase #5 $136.72   12.184%   $153.378   $153.38   $153.40   $153.40  
  Purchase #6 $171.75   12.157%   $192.6296   $192.63   $192.65   $192.60  
  Purchase #7 $145.40   7.752%   $156.6714   $156.67   $156.65   $156.70  
  7 purchase totals = $818.57       $914.2891   $914.30   $914.30   $914.40