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	$8.43	6.829%	$9.0057	$9.01	$9.00	$9.00
Purchase #2	$160.56	9.657%	$176.0653	$176.07	$176.05	$176.10
Purchase #3	$196.95	12.768%	$222.0966	$222.10	$222.10	$222.10
Purchase #4	$98.46	13.454%	$111.7068	$111.71	$111.70	$111.70
Purchase #5	$69.81	11.736%	$78.0029	$78.00	$78.00	$78.00
Purchase #6	$190.80	13.234%	$216.0505	$216.05	$216.05	$216.10
Purchase #7	$173.29	9.250%	$189.3193	$189.32	$189.30	$189.30
7 purchase totals =	$898.30		$1,002.2471	$1,002.26	$1,002.20	$1,002.30