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	$123.33	13.844%	$140.4038	$140.40	$140.40	$140.40
Purchase #2	$48.56	13.317%	$55.0267	$55.03	$55.05	$55.00
Purchase #3	$132.72	11.350%	$147.7837	$147.78	$147.80	$147.80
Purchase #4	$196.36	12.318%	$220.5476	$220.55	$220.55	$220.50
Purchase #5	$144.74	13.444%	$164.1988	$164.20	$164.20	$164.20
Purchase #6	$77.54	7.788%	$83.5788	$83.58	$83.60	$83.60
Purchase #7	$126.33	3.485%	$130.7326	$130.73	$130.75	$130.70
7 purchase totals =	$849.58		$942.2720	$942.27	$942.35	$942.20