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	$136.88	12.402%	$153.8559	$153.86	$153.85	$153.90
Purchase #2	$53.86	13.453%	$61.1058	$61.11	$61.10	$61.10
Purchase #3	$234.91	3.783%	$243.7966	$243.80	$243.80	$243.80
Purchase #4	$164.37	12.717%	$185.2729	$185.27	$185.25	$185.30
Purchase #5	$189.25	11.569%	$211.1443	$211.14	$211.15	$211.10
Purchase #6	$250.56	13.461%	$284.2879	$284.29	$284.30	$284.30
Purchase #7	$155.92	12.597%	$175.5612	$175.56	$175.55	$175.60
7 purchase totals =	$1,185.75		$1,315.0246	$1,315.03	$1,315.00	$1,315.10