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	$97.33	3.433%	$100.6713	$100.67	$100.65	$100.70
Purchase #2	$54.80	6.806%	$58.5297	$58.53	$58.55	$58.50
Purchase #3	$54.48	11.811%	$60.9146	$60.91	$60.90	$60.90
Purchase #4	$141.38	3.810%	$146.7666	$146.77	$146.75	$146.80
Purchase #5	$73.84	6.510%	$78.647	$78.65	$78.65	$78.60
Purchase #6	$157.68	7.119%	$168.9052	$168.91	$168.90	$168.90
Purchase #7	$233.49	4.463%	$243.9107	$243.91	$243.90	$243.90
7 purchase totals =	$813.00		$858.3451	$858.35	$858.30	$858.30