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	$37.72	3.721%	$39.1236	$39.12	$39.10	$39.10
Purchase #2	$140.34	4.320%	$146.4027	$146.40	$146.40	$146.40
Purchase #3	$63.51	6.401%	$67.5753	$67.58	$67.60	$67.60
Purchase #4	$78.98	4.607%	$82.6186	$82.62	$82.60	$82.60
Purchase #5	$135.50	10.297%	$149.4524	$149.45	$149.45	$149.50
Purchase #6	$67.77	4.802%	$71.0243	$71.02	$71.00	$71.00
Purchase #7	$243.71	9.496%	$266.8527	$266.85	$266.85	$266.90
7 purchase totals =	$767.53		$823.0496	$823.04	$823.00	$823.10