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	$33.66	6.163%	$35.7345	$35.73	$35.75	$35.70
Purchase #2	$202.95	9.612%	$222.4576	$222.46	$222.45	$222.50
Purchase #3	$124.36	13.791%	$141.5105	$141.51	$141.50	$141.50
Purchase #4	$54.72	4.135%	$56.9827	$56.98	$57.00	$57.00
Purchase #5	$39.52	10.803%	$43.7893	$43.79	$43.80	$43.80
Purchase #6	$165.32	5.736%	$174.8028	$174.80	$174.80	$174.80
Purchase #7	$46.63	13.259%	$52.8127	$52.81	$52.80	$52.80
7 purchase totals =	$667.16		$728.0901	$728.08	$728.10	$728.10