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	$31.48	11.260%	$35.0246	$35.02	$35.00	$35.00
Purchase #2	$137.58	6.386%	$146.3659	$146.37	$146.35	$146.40
Purchase #3	$233.76	12.813%	$263.7117	$263.71	$263.70	$263.70
Purchase #4	$170.46	5.140%	$179.2216	$179.22	$179.20	$179.20
Purchase #5	$81.95	10.501%	$90.5556	$90.56	$90.55	$90.60
Purchase #6	$137.70	5.219%	$144.8866	$144.89	$144.90	$144.90
Purchase #7	$60.45	6.491%	$64.3738	$64.37	$64.35	$64.40
7 purchase totals =	$853.38		$924.1398	$924.14	$924.05	$924.20