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 $227.96   12.426%   $256.2863   $256.29   $256.30   $256.30  
  Purchase #2 $151.55   3.813%   $157.3286   $157.33   $157.35   $157.30  
  Purchase #3 $68.57   11.286%   $76.3088   $76.31   $76.30   $76.30  
  Purchase #4 $92.33   8.504%   $100.1817   $100.18   $100.20   $100.20  
  Purchase #5 $7.42   4.488%   $7.753   $7.75   $7.75   $7.80  
  Purchase #6 $167.43   9.165%   $182.775   $182.78   $182.80   $182.80  
  Purchase #7 $231.55   7.529%   $248.9834   $248.98   $249.00   $249.00  
  7 purchase totals = $946.81       $1,029.6168   $1,029.62   $1,029.70   $1,029.70