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 $62.49   4.628%   $65.382   $65.38   $65.40   $65.40  
  Purchase #2 $195.51   3.607%   $202.562   $202.56   $202.55   $202.60  
  Purchase #3 $33.79   10.535%   $37.3498   $37.35   $37.35   $37.30  
  Purchase #4 $237.28   7.628%   $255.3797   $255.38   $255.40   $255.40  
  Purchase #5 $22.62   9.496%   $24.768   $24.77   $24.75   $24.80  
  Purchase #6 $105.83   11.247%   $117.7327   $117.73   $117.75   $117.70  
  Purchase #7 $198.65   13.431%   $225.3307   $225.33   $225.35   $225.30  
  7 purchase totals = $856.17       $928.5049   $928.50   $928.55   $928.50