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	$98.60	11.694%	$110.1303	$110.13	$110.15	$110.10
Purchase #2	$108.73	9.652%	$119.2246	$119.22	$119.20	$119.20
Purchase #3	$220.44	12.402%	$247.779	$247.78	$247.80	$247.80
Purchase #4	$77.48	11.642%	$86.5002	$86.50	$86.50	$86.50
Purchase #5	$118.70	8.468%	$128.7515	$128.75	$128.75	$128.80
Purchase #6	$80.32	11.116%	$89.2484	$89.25	$89.25	$89.20
Purchase #7	$182.45	7.764%	$196.6154	$196.62	$196.60	$196.60
7 purchase totals =	$886.72		$978.2494	$978.25	$978.25	$978.20