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	$136.80	9.748%	$150.1353	$150.14	$150.15	$150.10
Purchase #2	$51.56	6.126%	$54.7186	$54.72	$54.70	$54.70
Purchase #3	$243.38	6.783%	$259.8885	$259.89	$259.90	$259.90
Purchase #4	$147.85	12.211%	$165.904	$165.90	$165.90	$165.90
Purchase #5	$33.31	8.534%	$36.1527	$36.15	$36.15	$36.20
Purchase #6	$7.72	3.169%	$7.9646	$7.96	$7.95	$8.00
Purchase #7	$28.44	13.569%	$32.299	$32.30	$32.30	$32.30
7 purchase totals =	$649.06		$707.0627	$707.06	$707.05	$707.10