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	$64.87	11.426%	$72.282	$72.28	$72.30	$72.30
Purchase #2	$91.84	7.692%	$98.9043	$98.90	$98.90	$98.90
Purchase #3	$176.96	13.148%	$200.2267	$200.23	$200.25	$200.20
Purchase #4	$20.66	6.224%	$21.9459	$21.95	$21.95	$21.90
Purchase #5	$55.95	9.334%	$61.1724	$61.17	$61.15	$61.20
Purchase #6	$74.76	3.736%	$77.553	$77.55	$77.55	$77.60
Purchase #7	$55.91	8.267%	$60.5321	$60.53	$60.55	$60.50
7 purchase totals =	$540.95		$592.6164	$592.61	$592.65	$592.60