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 $44.61   4.758%   $46.7325   $46.73   $46.75   $46.70  
  Purchase #2 $19.70   7.814%   $21.2394   $21.24   $21.25   $21.20  
  Purchase #3 $193.79   13.722%   $220.3819   $220.38   $220.40   $220.40  
  Purchase #4 $245.77   7.143%   $263.3254   $263.33   $263.35   $263.30  
  Purchase #5 $233.88   12.139%   $262.2707   $262.27   $262.25   $262.30  
  Purchase #6 $160.73   3.274%   $165.9923   $165.99   $166.00   $166.00  
  Purchase #7 $79.48   4.669%   $83.1909   $83.19   $83.20   $83.20  
  7 purchase totals = $977.96       $1,063.1331   $1,063.13   $1,063.20   $1,063.10