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	$104.83	4.443%	$109.4876	$109.49	$109.50	$109.50
Purchase #2	$83.72	5.137%	$88.0207	$88.02	$88.00	$88.00
Purchase #3	$45.75	3.587%	$47.3911	$47.39	$47.40	$47.40
Purchase #4	$68.31	11.689%	$76.2948	$76.29	$76.30	$76.30
Purchase #5	$8.84	4.143%	$9.2062	$9.21	$9.20	$9.20
Purchase #6	$189.90	3.433%	$196.4193	$196.42	$196.40	$196.40
Purchase #7	$58.27	11.369%	$64.8947	$64.89	$64.90	$64.90
7 purchase totals =	$559.62		$591.7144	$591.71	$591.70	$591.70