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	$139.43	4.817%	$146.1463	$146.15	$146.15	$146.10
Purchase #2	$179.63	3.230%	$185.432	$185.43	$185.45	$185.40
Purchase #3	$172.32	10.572%	$190.5377	$190.54	$190.55	$190.50
Purchase #4	$99.30	8.248%	$107.4903	$107.49	$107.50	$107.50
Purchase #5	$194.77	9.631%	$213.5283	$213.53	$213.55	$213.50
Purchase #6	$22.67	9.571%	$24.8397	$24.84	$24.85	$24.80
Purchase #7	$194.61	7.819%	$209.8266	$209.83	$209.85	$209.80
7 purchase totals =	$1,002.73		$1,077.8009	$1,077.81	$1,077.90	$1,077.60