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	$7.73	10.262%	$8.5233	$8.52	$8.50	$8.50
Purchase #2	$171.40	11.110%	$190.4425	$190.44	$190.45	$190.40
Purchase #3	$167.91	4.769%	$175.9176	$175.92	$175.90	$175.90
Purchase #4	$74.71	11.751%	$83.4892	$83.49	$83.50	$83.50
Purchase #5	$26.77	6.559%	$28.5258	$28.53	$28.55	$28.50
Purchase #6	$62.60	5.132%	$65.8126	$65.81	$65.80	$65.80
Purchase #7	$223.83	4.121%	$233.054	$233.05	$233.05	$233.10
7 purchase totals =	$734.95		$785.7650	$785.76	$785.75	$785.70