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	$27.93	13.612%	$31.7318	$31.73	$31.75	$31.70
Purchase #2	$38.68	3.431%	$40.0071	$40.01	$40.00	$40.00
Purchase #3	$98.66	11.318%	$109.8263	$109.83	$109.85	$109.80
Purchase #4	$222.27	9.785%	$244.0191	$244.02	$244.00	$244.00
Purchase #5	$158.33	5.420%	$166.9115	$166.91	$166.90	$166.90
Purchase #6	$144.80	6.196%	$153.7718	$153.77	$153.75	$153.80
Purchase #7	$30.90	13.850%	$35.1797	$35.18	$35.20	$35.20
7 purchase totals =	$721.57		$781.4473	$781.45	$781.45	$781.40