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 $233.95   6.447%   $249.0328   $249.03   $249.05   $249.00  
  Purchase #2 $5.70   11.247%   $6.3411   $6.34   $6.35   $6.30  
  Purchase #3 $189.38   10.354%   $208.9884   $208.99   $209.00   $209.00  
  Purchase #4 $114.41   10.453%   $126.3693   $126.37   $126.35   $126.40  
  Purchase #5 $21.65   12.582%   $24.374   $24.37   $24.35   $24.40  
  Purchase #6 $193.58   8.833%   $210.6789   $210.68   $210.70   $210.70  
  Purchase #7 $207.75   8.809%   $226.0507   $226.05   $226.05   $226.10  
  7 purchase totals = $966.42       $1,051.8352   $1,051.83   $1,051.85   $1,051.90