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	$82.92	5.309%	$87.3222	$87.32	$87.30	$87.30
Purchase #2	$209.25	6.674%	$223.2153	$223.22	$223.20	$223.20
Purchase #3	$92.52	12.849%	$104.4079	$104.41	$104.40	$104.40
Purchase #4	$175.42	5.300%	$184.7173	$184.72	$184.70	$184.70
Purchase #5	$159.51	5.718%	$168.6308	$168.63	$168.65	$168.60
Purchase #6	$119.66	7.142%	$128.2061	$128.21	$128.20	$128.20
Purchase #7	$195.88	13.862%	$223.0329	$223.03	$223.05	$223.00
7 purchase totals =	$1,035.16		$1,119.5325	$1,119.54	$1,119.50	$1,119.40