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 $206.85   12.726%   $233.1737   $233.17   $233.15   $233.20  
  Purchase #2 $6.99   4.372%   $7.2956   $7.30   $7.30   $7.30  
  Purchase #3 $225.25   5.203%   $236.9698   $236.97   $236.95   $237.00  
  Purchase #4 $165.78   9.355%   $181.2887   $181.29   $181.30   $181.30  
  Purchase #5 $156.46   3.710%   $162.2647   $162.26   $162.25   $162.30  
  Purchase #6 $32.82   11.422%   $36.5687   $36.57   $36.55   $36.60  
  Purchase #7 $156.53   12.150%   $175.5484   $175.55   $175.55   $175.50  
  7 purchase totals = $950.68       $1,033.1096   $1,033.11   $1,033.05   $1,033.20