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	$120.58	13.228%	$136.5303	$136.53	$136.55	$136.50
Purchase #2	$100.49	6.475%	$106.9967	$107.00	$107.00	$107.00
Purchase #3	$83.52	8.644%	$90.7395	$90.74	$90.75	$90.70
Purchase #4	$35.96	4.214%	$37.4754	$37.48	$37.50	$37.50
Purchase #5	$245.49	3.490%	$254.0576	$254.06	$254.05	$254.10
Purchase #6	$73.41	13.409%	$83.2535	$83.25	$83.25	$83.30
Purchase #7	$206.28	7.668%	$222.0976	$222.10	$222.10	$222.10
7 purchase totals =	$865.73		$931.1506	$931.16	$931.20	$931.20