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	$37.83	8.583%	$41.0769	$41.08	$41.10	$41.10
Purchase #2	$168.97	12.759%	$190.5289	$190.53	$190.55	$190.50
Purchase #3	$82.99	7.802%	$89.4649	$89.46	$89.45	$89.50
Purchase #4	$236.96	6.174%	$251.5899	$251.59	$251.60	$251.60
Purchase #5	$173.50	6.385%	$184.578	$184.58	$184.60	$184.60
Purchase #6	$224.31	10.872%	$248.697	$248.70	$248.70	$248.70
Purchase #7	$71.43	9.675%	$78.3409	$78.34	$78.35	$78.30
7 purchase totals =	$995.99		$1,084.2765	$1,084.28	$1,084.35	$1,084.30