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	$86.83	6.284%	$92.2864	$92.29	$92.30	$92.30
Purchase #2	$94.59	7.640%	$101.8167	$101.82	$101.80	$101.80
Purchase #3	$76.25	3.449%	$78.8799	$78.88	$78.90	$78.90
Purchase #4	$239.31	9.529%	$262.1138	$262.11	$262.10	$262.10
Purchase #5	$129.50	13.726%	$147.2752	$147.28	$147.30	$147.30
Purchase #6	$68.47	4.546%	$71.5826	$71.58	$71.60	$71.60
Purchase #7	$74.42	3.389%	$76.9421	$76.94	$76.95	$76.90
7 purchase totals =	$769.37		$830.8967	$830.90	$830.95	$830.90