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	$104.82	5.674%	$110.7675	$110.77	$110.75	$110.80
Purchase #2	$134.55	7.452%	$144.5767	$144.58	$144.60	$144.60
Purchase #3	$36.46	9.501%	$39.9241	$39.92	$39.90	$39.90
Purchase #4	$61.50	9.821%	$67.5399	$67.54	$67.55	$67.50
Purchase #5	$40.79	12.108%	$45.7289	$45.73	$45.75	$45.70
Purchase #6	$61.58	7.422%	$66.1505	$66.15	$66.15	$66.20
Purchase #7	$194.84	7.435%	$209.3264	$209.33	$209.35	$209.30
7 purchase totals =	$634.54		$684.0140	$684.02	$684.05	$684.00