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	$138.70	12.857%	$156.5327	$156.53	$156.55	$156.50
Purchase #2	$217.97	11.730%	$243.5379	$243.54	$243.55	$243.50
Purchase #3	$141.28	8.410%	$153.1616	$153.16	$153.15	$153.20
Purchase #4	$198.86	11.636%	$221.9993	$222.00	$222.00	$222.00
Purchase #5	$76.41	9.515%	$83.6804	$83.68	$83.70	$83.70
Purchase #6	$231.71	8.294%	$250.928	$250.93	$250.95	$250.90
Purchase #7	$56.80	7.864%	$61.2668	$61.27	$61.25	$61.30
7 purchase totals =	$1,061.73		$1,171.1067	$1,171.11	$1,171.15	$1,171.10