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	$49.56	5.196%	$52.1351	$52.14	$52.15	$52.10
Purchase #2	$26.78	8.847%	$29.1492	$29.15	$29.15	$29.10
Purchase #3	$250.36	7.487%	$269.1045	$269.10	$269.10	$269.10
Purchase #4	$78.66	13.528%	$89.3011	$89.30	$89.30	$89.30
Purchase #5	$89.55	13.820%	$101.9258	$101.93	$101.95	$101.90
Purchase #6	$201.98	8.849%	$219.8532	$219.85	$219.85	$219.90
Purchase #7	$191.85	13.601%	$217.9435	$217.94	$217.95	$217.90
7 purchase totals =	$888.74		$979.4124	$979.41	$979.45	$979.30