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	$73.62	13.427%	$83.505	$83.51	$83.50	$83.50
Purchase #2	$154.26	10.501%	$170.4588	$170.46	$170.45	$170.50
Purchase #3	$160.41	4.192%	$167.1344	$167.13	$167.15	$167.10
Purchase #4	$56.34	11.520%	$62.8304	$62.83	$62.85	$62.80
Purchase #5	$113.36	5.432%	$119.5177	$119.52	$119.50	$119.50
Purchase #6	$37.54	11.453%	$41.8395	$41.84	$41.85	$41.80
Purchase #7	$225.81	13.254%	$255.7389	$255.74	$255.75	$255.70
7 purchase totals =	$821.34		$901.0247	$901.03	$901.05	$900.90