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	$129.52	6.366%	$137.7652	$137.77	$137.75	$137.80
Purchase #2	$154.77	11.131%	$171.9974	$172.00	$172.00	$172.00
Purchase #3	$165.89	3.432%	$171.5833	$171.58	$171.60	$171.60
Purchase #4	$73.51	4.117%	$76.5364	$76.54	$76.55	$76.50
Purchase #5	$225.47	11.165%	$250.6437	$250.64	$250.65	$250.60
Purchase #6	$113.63	4.284%	$118.4979	$118.50	$118.50	$118.50
Purchase #7	$104.98	13.373%	$119.019	$119.02	$119.00	$119.00
7 purchase totals =	$967.77		$1,046.0429	$1,046.05	$1,046.05	$1,046.00