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	$199.29	12.849%	$224.8968	$224.90	$224.90	$224.90
Purchase #2	$74.28	12.756%	$83.7552	$83.76	$83.75	$83.80
Purchase #3	$96.55	3.866%	$100.2826	$100.28	$100.30	$100.30
Purchase #4	$134.84	5.568%	$142.3479	$142.35	$142.35	$142.30
Purchase #5	$159.40	8.444%	$172.8597	$172.86	$172.85	$172.90
Purchase #6	$30.45	10.780%	$33.7325	$33.73	$33.75	$33.70
Purchase #7	$203.81	11.872%	$228.0063	$228.01	$228.00	$228.00
7 purchase totals =	$898.62		$985.8810	$985.89	$985.90	$985.90