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	$112.82	6.641%	$120.3124	$120.31	$120.30	$120.30
Purchase #2	$66.33	4.789%	$69.5065	$69.51	$69.50	$69.50
Purchase #3	$141.53	11.568%	$157.9022	$157.90	$157.90	$157.90
Purchase #4	$123.51	11.207%	$137.3518	$137.35	$137.35	$137.40
Purchase #5	$231.52	4.576%	$242.1144	$242.11	$242.10	$242.10
Purchase #6	$29.71	9.408%	$32.5051	$32.51	$32.50	$32.50
Purchase #7	$111.30	4.630%	$116.4532	$116.45	$116.45	$116.50
7 purchase totals =	$816.72		$876.1456	$876.14	$876.10	$876.20