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	$222.37	8.487%	$241.2425	$241.24	$241.25	$241.20
Purchase #2	$79.55	12.799%	$89.7316	$89.73	$89.75	$89.70
Purchase #3	$157.68	12.779%	$177.8299	$177.83	$177.85	$177.80
Purchase #4	$11.95	12.700%	$13.4677	$13.47	$13.45	$13.50
Purchase #5	$171.96	6.376%	$182.9242	$182.92	$182.90	$182.90
Purchase #6	$107.25	11.789%	$119.8937	$119.89	$119.90	$119.90
Purchase #7	$111.83	7.871%	$120.6321	$120.63	$120.65	$120.60
7 purchase totals =	$862.59		$945.7217	$945.71	$945.75	$945.60