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	$81.72	8.808%	$88.9179	$88.92	$88.90	$88.90
Purchase #2	$160.56	4.651%	$168.0276	$168.03	$168.05	$168.00
Purchase #3	$210.55	13.677%	$239.3469	$239.35	$239.35	$239.30
Purchase #4	$80.74	7.548%	$86.8343	$86.83	$86.85	$86.80
Purchase #5	$37.89	11.633%	$42.2977	$42.30	$42.30	$42.30
Purchase #6	$106.36	6.525%	$113.3	$113.30	$113.30	$113.30
Purchase #7	$62.33	4.826%	$65.338	$65.34	$65.35	$65.30
7 purchase totals =	$740.15		$804.0624	$804.07	$804.10	$803.90