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	$127.34	13.203%	$144.1527	$144.15	$144.15	$144.20
Purchase #2	$211.79	5.724%	$223.9129	$223.91	$223.90	$223.90
Purchase #3	$132.86	3.579%	$137.6151	$137.62	$137.60	$137.60
Purchase #4	$201.66	3.797%	$209.317	$209.32	$209.30	$209.30
Purchase #5	$145.41	6.520%	$154.8907	$154.89	$154.90	$154.90
Purchase #6	$120.29	9.693%	$131.9497	$131.95	$131.95	$131.90
Purchase #7	$84.25	5.281%	$88.6992	$88.70	$88.70	$88.70
7 purchase totals =	$1,023.60		$1,090.5373	$1,090.54	$1,090.50	$1,090.50