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	$188.97	10.744%	$209.2729	$209.27	$209.25	$209.30
Purchase #2	$25.25	8.426%	$27.3776	$27.38	$27.40	$27.40
Purchase #3	$230.68	8.588%	$250.4908	$250.49	$250.50	$250.50
Purchase #4	$105.33	10.269%	$116.1463	$116.15	$116.15	$116.10
Purchase #5	$179.64	3.135%	$185.2717	$185.27	$185.25	$185.30
Purchase #6	$99.98	9.149%	$109.1272	$109.13	$109.15	$109.10
Purchase #7	$171.26	8.855%	$186.4251	$186.43	$186.45	$186.40
7 purchase totals =	$1,001.11		$1,084.1116	$1,084.12	$1,084.15	$1,084.10