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	$138.55	6.745%	$147.8952	$147.90	$147.90	$147.90
Purchase #2	$92.34	10.298%	$101.8492	$101.85	$101.85	$101.80
Purchase #3	$236.82	12.501%	$266.4249	$266.42	$266.40	$266.40
Purchase #4	$36.58	9.656%	$40.1122	$40.11	$40.10	$40.10
Purchase #5	$88.89	8.469%	$96.4181	$96.42	$96.40	$96.40
Purchase #6	$129.87	13.111%	$146.8973	$146.90	$146.90	$146.90
Purchase #7	$113.84	13.229%	$128.8999	$128.90	$128.90	$128.90
7 purchase totals =	$836.89		$928.4968	$928.50	$928.45	$928.40