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	$45.29	10.867%	$50.2117	$50.21	$50.20	$50.20
Purchase #2	$135.41	3.164%	$139.6944	$139.69	$139.70	$139.70
Purchase #3	$24.77	4.541%	$25.8948	$25.89	$25.90	$25.90
Purchase #4	$86.50	10.803%	$95.8446	$95.84	$95.85	$95.80
Purchase #5	$134.71	7.687%	$145.0652	$145.07	$145.05	$145.10
Purchase #6	$130.77	8.516%	$141.9064	$141.91	$141.90	$141.90
Purchase #7	$78.32	8.501%	$84.978	$84.98	$85.00	$85.00
7 purchase totals =	$635.77		$683.5951	$683.59	$683.60	$683.60