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 $44.90   13.621%   $51.0158   $51.02   $51.00   $51.00  
  Purchase #2 $202.44   3.568%   $209.6631   $209.66   $209.65   $209.70  
  Purchase #3 $23.34   8.292%   $25.2754   $25.28   $25.30   $25.30  
  Purchase #4 $32.64   4.683%   $34.1685   $34.17   $34.15   $34.20  
  Purchase #5 $227.76   5.203%   $239.6104   $239.61   $239.60   $239.60  
  Purchase #6 $233.50   10.809%   $258.739   $258.74   $258.75   $258.70  
  Purchase #7 $195.65   7.774%   $210.8598   $210.86   $210.85   $210.90  
  7 purchase totals = $960.23       $1,029.3320   $1,029.34   $1,029.30   $1,029.40