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	$103.27	11.502%	$115.1481	$115.15	$115.15	$115.10
Purchase #2	$36.56	12.762%	$41.2258	$41.23	$41.25	$41.20
Purchase #3	$112.92	13.255%	$127.8875	$127.89	$127.90	$127.90
Purchase #4	$233.88	5.404%	$246.5189	$246.52	$246.50	$246.50
Purchase #5	$149.26	10.186%	$164.4636	$164.46	$164.45	$164.50
Purchase #6	$156.25	11.612%	$174.3938	$174.39	$174.40	$174.40
Purchase #7	$22.88	10.647%	$25.316	$25.32	$25.30	$25.30
7 purchase totals =	$815.02		$894.9537	$894.96	$894.95	$894.90