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	$80.35	4.445%	$83.9216	$83.92	$83.90	$83.90
Purchase #2	$156.43	3.842%	$162.44	$162.44	$162.45	$162.40
Purchase #3	$172.69	11.201%	$192.033	$192.03	$192.05	$192.00
Purchase #4	$193.91	6.352%	$206.2272	$206.23	$206.25	$206.20
Purchase #5	$130.56	10.681%	$144.5051	$144.51	$144.50	$144.50
Purchase #6	$45.43	5.813%	$48.0708	$48.07	$48.05	$48.10
Purchase #7	$78.86	8.637%	$85.6711	$85.67	$85.65	$85.70
7 purchase totals =	$858.23		$922.8688	$922.87	$922.85	$922.80