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	$170.45	5.792%	$180.3225	$180.32	$180.30	$180.30
Purchase #2	$184.89	13.512%	$209.8723	$209.87	$209.85	$209.90
Purchase #3	$16.42	6.515%	$17.4898	$17.49	$17.50	$17.50
Purchase #4	$77.48	10.775%	$85.8285	$85.83	$85.85	$85.80
Purchase #5	$222.48	12.751%	$250.8484	$250.85	$250.85	$250.80
Purchase #6	$196.34	8.174%	$212.3888	$212.39	$212.40	$212.40
Purchase #7	$49.75	12.382%	$55.91	$55.91	$55.90	$55.90
7 purchase totals =	$917.81		$1,012.6603	$1,012.66	$1,012.65	$1,012.60