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	$189.41	12.586%	$213.2491	$213.25	$213.25	$213.20
Purchase #2	$17.36	8.838%	$18.8943	$18.89	$18.90	$18.90
Purchase #3	$219.54	6.413%	$233.6191	$233.62	$233.60	$233.60
Purchase #4	$231.44	4.773%	$242.4866	$242.49	$242.50	$242.50
Purchase #5	$123.36	7.867%	$133.0647	$133.06	$133.05	$133.10
Purchase #6	$17.69	10.735%	$19.589	$19.59	$19.60	$19.60
Purchase #7	$93.77	7.271%	$100.588	$100.59	$100.60	$100.60
7 purchase totals =	$892.57		$961.4908	$961.49	$961.50	$961.50