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	$145.61	6.707%	$155.3761	$155.38	$155.40	$155.40
Purchase #2	$96.69	4.575%	$101.1136	$101.11	$101.10	$101.10
Purchase #3	$36.67	9.504%	$40.1551	$40.16	$40.15	$40.20
Purchase #4	$245.39	8.165%	$265.4261	$265.43	$265.45	$265.40
Purchase #5	$157.54	5.552%	$166.2866	$166.29	$166.30	$166.30
Purchase #6	$213.30	8.871%	$232.2218	$232.22	$232.20	$232.20
Purchase #7	$83.42	8.674%	$90.6559	$90.66	$90.65	$90.70
7 purchase totals =	$978.62		$1,051.2352	$1,051.25	$1,051.25	$1,051.30