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 $247.37   8.411%   $268.1763   $268.18   $268.20   $268.20  
  Purchase #2 $65.92   10.623%   $72.9227   $72.92   $72.90   $72.90  
  Purchase #3 $241.65   6.581%   $257.553   $257.55   $257.55   $257.60  
  Purchase #4 $190.48   9.301%   $208.1965   $208.20   $208.20   $208.20  
  Purchase #5 $101.36   4.145%   $105.5614   $105.56   $105.55   $105.60  
  Purchase #6 $129.89   11.138%   $144.3571   $144.36   $144.35   $144.40  
  Purchase #7 $199.88   4.726%   $209.3263   $209.33   $209.35   $209.30  
  7 purchase totals = $1,176.55       $1,266.0933   $1,266.10   $1,266.10   $1,266.20