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	$237.91	6.679%	$253.8	$253.80	$253.80	$253.80
Purchase #2	$227.79	13.790%	$259.2022	$259.20	$259.20	$259.20
Purchase #3	$204.64	10.212%	$225.5378	$225.54	$225.55	$225.50
Purchase #4	$134.76	13.150%	$152.4809	$152.48	$152.50	$152.50
Purchase #5	$145.42	5.103%	$152.8408	$152.84	$152.85	$152.80
Purchase #6	$95.62	6.779%	$102.1021	$102.10	$102.10	$102.10
Purchase #7	$6.40	7.655%	$6.8899	$6.89	$6.90	$6.90
7 purchase totals =	$1,052.54		$1,152.8537	$1,152.85	$1,152.90	$1,152.80