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	$248.34	3.169%	$256.2099	$256.21	$256.20	$256.20
Purchase #2	$187.50	5.714%	$198.2138	$198.21	$198.20	$198.20
Purchase #3	$123.96	5.864%	$131.229	$131.23	$131.25	$131.20
Purchase #4	$183.32	9.462%	$200.6657	$200.67	$200.65	$200.70
Purchase #5	$122.36	7.530%	$131.5737	$131.57	$131.55	$131.60
Purchase #6	$145.89	6.614%	$155.5392	$155.54	$155.55	$155.50
Purchase #7	$248.28	11.705%	$277.3412	$277.34	$277.35	$277.30
7 purchase totals =	$1,259.65		$1,350.7725	$1,350.77	$1,350.75	$1,350.70