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	$34.35	10.281%	$37.8815	$37.88	$37.90	$37.90
Purchase #2	$245.51	4.597%	$256.7961	$256.80	$256.80	$256.80
Purchase #3	$185.56	10.824%	$205.645	$205.65	$205.65	$205.60
Purchase #4	$50.63	8.685%	$55.0272	$55.03	$55.05	$55.00
Purchase #5	$216.63	12.839%	$244.4431	$244.44	$244.45	$244.40
Purchase #6	$215.74	11.579%	$240.7205	$240.72	$240.70	$240.70
Purchase #7	$132.39	9.871%	$145.4582	$145.46	$145.45	$145.50
7 purchase totals =	$1,080.81		$1,185.9716	$1,185.98	$1,186.00	$1,185.90