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	$119.93	12.464%	$134.8781	$134.88	$134.90	$134.90
Purchase #2	$69.35	3.109%	$71.5061	$71.51	$71.50	$71.50
Purchase #3	$99.89	11.667%	$111.5442	$111.54	$111.55	$111.50
Purchase #4	$7.41	8.575%	$8.0454	$8.05	$8.05	$8.00
Purchase #5	$224.54	11.714%	$250.8426	$250.84	$250.85	$250.80
Purchase #6	$32.73	13.377%	$37.1083	$37.11	$37.10	$37.10
Purchase #7	$31.34	3.478%	$32.43	$32.43	$32.45	$32.40
7 purchase totals =	$585.19		$646.3547	$646.36	$646.40	$646.20