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	$100.92	3.318%	$104.2685	$104.27	$104.25	$104.30
Purchase #2	$153.98	11.418%	$171.5614	$171.56	$171.55	$171.60
Purchase #3	$221.94	7.817%	$239.289	$239.29	$239.30	$239.30
Purchase #4	$29.45	12.569%	$33.1516	$33.15	$33.15	$33.20
Purchase #5	$134.67	12.145%	$151.0257	$151.03	$151.05	$151.00
Purchase #6	$172.47	13.744%	$196.1743	$196.17	$196.15	$196.20
Purchase #7	$228.31	9.392%	$249.7529	$249.75	$249.75	$249.80
7 purchase totals =	$1,041.74		$1,145.2234	$1,145.22	$1,145.20	$1,145.40