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	$123.56	5.316%	$130.1284	$130.13	$130.15	$130.10
Purchase #2	$216.50	6.587%	$230.7609	$230.76	$230.75	$230.80
Purchase #3	$173.28	6.121%	$183.8865	$183.89	$183.90	$183.90
Purchase #4	$91.43	11.865%	$102.2782	$102.28	$102.30	$102.30
Purchase #5	$29.58	5.492%	$31.2045	$31.20	$31.20	$31.20
Purchase #6	$132.43	5.490%	$139.7004	$139.70	$139.70	$139.70
Purchase #7	$168.83	9.782%	$185.345	$185.35	$185.35	$185.30
7 purchase totals =	$935.61		$1,003.3039	$1,003.31	$1,003.35	$1,003.30