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	$99.65	4.404%	$104.0386	$104.04	$104.05	$104.00
Purchase #2	$72.55	9.189%	$79.2166	$79.22	$79.20	$79.20
Purchase #3	$243.50	13.315%	$275.922	$275.92	$275.90	$275.90
Purchase #4	$91.62	5.752%	$96.89	$96.89	$96.90	$96.90
Purchase #5	$150.68	10.507%	$166.5119	$166.51	$166.50	$166.50
Purchase #6	$82.39	6.446%	$87.7009	$87.70	$87.70	$87.70
Purchase #7	$90.33	4.220%	$94.1419	$94.14	$94.15	$94.10
7 purchase totals =	$830.72		$904.4219	$904.42	$904.40	$904.30