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	$166.80	12.774%	$188.107	$188.11	$188.10	$188.10
Purchase #2	$104.43	4.334%	$108.956	$108.96	$108.95	$109.00
Purchase #3	$60.27	7.699%	$64.9102	$64.91	$64.90	$64.90
Purchase #4	$33.89	11.533%	$37.7985	$37.80	$37.80	$37.80
Purchase #5	$135.26	7.823%	$145.8414	$145.84	$145.85	$145.80
Purchase #6	$98.57	12.621%	$111.0105	$111.01	$111.00	$111.00
Purchase #7	$119.25	3.182%	$123.0445	$123.04	$123.05	$123.00
7 purchase totals =	$718.47		$779.6681	$779.67	$779.65	$779.60