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	$42.68	6.241%	$45.3437	$45.34	$45.35	$45.30
Purchase #2	$32.55	10.231%	$35.8802	$35.88	$35.90	$35.90
Purchase #3	$85.62	6.414%	$91.1117	$91.11	$91.10	$91.10
Purchase #4	$38.76	10.260%	$42.7368	$42.74	$42.75	$42.70
Purchase #5	$32.45	4.688%	$33.9713	$33.97	$33.95	$34.00
Purchase #6	$57.52	3.331%	$59.436	$59.44	$59.45	$59.40
Purchase #7	$11.53	5.556%	$12.1706	$12.17	$12.15	$12.20
7 purchase totals =	$301.11		$320.6503	$320.65	$320.65	$320.60