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	$198.84	13.606%	$225.8942	$225.89	$225.90	$225.90
Purchase #2	$214.59	11.307%	$238.8537	$238.85	$238.85	$238.90
Purchase #3	$72.56	8.155%	$78.4773	$78.48	$78.50	$78.50
Purchase #4	$182.91	9.621%	$200.5078	$200.51	$200.50	$200.50
Purchase #5	$202.40	11.297%	$225.2651	$225.27	$225.25	$225.30
Purchase #6	$32.41	3.741%	$33.6225	$33.62	$33.60	$33.60
Purchase #7	$131.79	10.113%	$145.1179	$145.12	$145.10	$145.10
7 purchase totals =	$1,035.50		$1,147.7385	$1,147.74	$1,147.70	$1,147.80