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	$69.78	13.102%	$78.9226	$78.92	$78.90	$78.90
Purchase #2	$88.64	12.485%	$99.7067	$99.71	$99.70	$99.70
Purchase #3	$126.43	6.427%	$134.5557	$134.56	$134.55	$134.60
Purchase #4	$149.91	6.111%	$159.071	$159.07	$159.05	$159.10
Purchase #5	$42.25	11.600%	$47.151	$47.15	$47.15	$47.20
Purchase #6	$168.25	8.616%	$182.7464	$182.75	$182.75	$182.70
Purchase #7	$221.62	3.393%	$229.1396	$229.14	$229.15	$229.10
7 purchase totals =	$866.88		$931.2930	$931.30	$931.25	$931.30