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	$110.96	8.502%	$120.3938	$120.39	$120.40	$120.40
Purchase #2	$202.50	5.422%	$213.4796	$213.48	$213.50	$213.50
Purchase #3	$111.72	6.722%	$119.2298	$119.23	$119.25	$119.20
Purchase #4	$5.66	8.842%	$6.1605	$6.16	$6.15	$6.20
Purchase #5	$104.52	4.756%	$109.491	$109.49	$109.50	$109.50
Purchase #6	$68.32	6.136%	$72.5121	$72.51	$72.50	$72.50
Purchase #7	$165.88	4.741%	$173.7444	$173.74	$173.75	$173.70
7 purchase totals =	$769.56		$815.0112	$815.00	$815.05	$815.00