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	$30.84	4.510%	$32.2309	$32.23	$32.25	$32.20
Purchase #2	$99.73	6.641%	$106.3531	$106.35	$106.35	$106.40
Purchase #3	$106.50	4.737%	$111.5449	$111.54	$111.55	$111.50
Purchase #4	$159.44	8.313%	$172.6942	$172.69	$172.70	$172.70
Purchase #5	$246.51	8.633%	$267.7912	$267.79	$267.80	$267.80
Purchase #6	$136.40	4.456%	$142.478	$142.48	$142.50	$142.50
Purchase #7	$88.98	10.236%	$98.088	$98.09	$98.10	$98.10
7 purchase totals =	$868.40		$931.1803	$931.17	$931.25	$931.20