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 $62.98   5.854%   $66.6668   $66.67   $66.65   $66.70  
  Purchase #2 $32.30   8.146%   $34.9312   $34.93   $34.95   $34.90  
  Purchase #3 $72.99   8.492%   $79.1883   $79.19   $79.20   $79.20  
  Purchase #4 $231.29   7.408%   $248.424   $248.42   $248.40   $248.40  
  Purchase #5 $246.38   12.488%   $277.1479   $277.15   $277.15   $277.10  
  Purchase #6 $167.85   3.244%   $173.2951   $173.30   $173.30   $173.30  
  Purchase #7 $159.90   11.839%   $178.8306   $178.83   $178.85   $178.80  
  7 purchase totals = $973.69       $1,058.4839   $1,058.49   $1,058.50   $1,058.40