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	$154.64	12.443%	$173.8819	$173.88	$173.90	$173.90
Purchase #2	$223.70	4.115%	$232.9053	$232.91	$232.90	$232.90
Purchase #3	$233.86	3.496%	$242.0357	$242.04	$242.05	$242.00
Purchase #4	$83.82	13.811%	$95.3964	$95.40	$95.40	$95.40
Purchase #5	$126.46	12.390%	$142.1284	$142.13	$142.15	$142.10
Purchase #6	$162.89	5.705%	$172.1829	$172.18	$172.20	$172.20
Purchase #7	$106.81	4.589%	$111.7115	$111.71	$111.70	$111.70
7 purchase totals =	$1,092.18		$1,170.2421	$1,170.25	$1,170.30	$1,170.20