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	$175.52	3.564%	$181.7755	$181.78	$181.80	$181.80
Purchase #2	$78.37	13.712%	$89.1161	$89.12	$89.10	$89.10
Purchase #3	$212.35	7.858%	$229.0365	$229.04	$229.05	$229.00
Purchase #4	$147.32	11.763%	$164.6493	$164.65	$164.65	$164.60
Purchase #5	$217.92	3.194%	$224.8804	$224.88	$224.90	$224.90
Purchase #6	$27.52	5.294%	$28.9769	$28.98	$29.00	$29.00
Purchase #7	$61.88	6.301%	$65.7791	$65.78	$65.80	$65.80
7 purchase totals =	$920.88		$984.2138	$984.23	$984.30	$984.20