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	$6.60	5.851%	$6.9862	$6.99	$7.00	$7.00
Purchase #2	$228.92	6.864%	$244.6331	$244.63	$244.65	$244.60
Purchase #3	$145.76	4.436%	$152.2259	$152.23	$152.25	$152.20
Purchase #4	$55.72	5.301%	$58.6737	$58.67	$58.65	$58.70
Purchase #5	$237.50	6.856%	$253.783	$253.78	$253.80	$253.80
Purchase #6	$53.78	12.465%	$60.4837	$60.48	$60.50	$60.50
Purchase #7	$80.55	11.150%	$89.5313	$89.53	$89.55	$89.50
7 purchase totals =	$808.83		$866.3169	$866.31	$866.40	$866.30