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	$154.57	7.712%	$166.4904	$166.49	$166.50	$166.50
Purchase #2	$204.89	5.769%	$216.7101	$216.71	$216.70	$216.70
Purchase #3	$203.32	4.328%	$212.1197	$212.12	$212.10	$212.10
Purchase #4	$69.41	13.700%	$78.9192	$78.92	$78.90	$78.90
Purchase #5	$160.74	7.568%	$172.9048	$172.90	$172.90	$172.90
Purchase #6	$21.58	3.725%	$22.3839	$22.38	$22.40	$22.40
Purchase #7	$233.35	13.377%	$264.5652	$264.57	$264.55	$264.60
7 purchase totals =	$1,047.86		$1,134.0933	$1,134.09	$1,134.05	$1,134.10