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	$202.46	13.648%	$230.0917	$230.09	$230.10	$230.10
Purchase #2	$120.98	6.190%	$128.4687	$128.47	$128.45	$128.50
Purchase #3	$157.63	6.661%	$168.1297	$168.13	$168.15	$168.10
Purchase #4	$35.44	12.134%	$39.7403	$39.74	$39.75	$39.70
Purchase #5	$122.59	4.788%	$128.4596	$128.46	$128.45	$128.50
Purchase #6	$60.84	4.741%	$63.7244	$63.72	$63.70	$63.70
Purchase #7	$85.91	4.214%	$89.5302	$89.53	$89.55	$89.50
7 purchase totals =	$785.85		$848.1446	$848.14	$848.15	$848.10