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	$179.42	6.851%	$191.7121	$191.71	$191.70	$191.70
Purchase #2	$124.59	12.871%	$140.626	$140.63	$140.65	$140.60
Purchase #3	$90.51	13.841%	$103.0375	$103.04	$103.05	$103.00
Purchase #4	$186.47	9.518%	$204.2182	$204.22	$204.20	$204.20
Purchase #5	$34.61	9.558%	$37.918	$37.92	$37.90	$37.90
Purchase #6	$75.86	13.108%	$85.8037	$85.80	$85.80	$85.80
Purchase #7	$123.66	5.804%	$130.8372	$130.84	$130.85	$130.80
7 purchase totals =	$815.12		$894.1527	$894.16	$894.15	$894.00