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	$250.91	13.839%	$285.6334	$285.63	$285.65	$285.60
Purchase #2	$81.74	11.135%	$90.8417	$90.84	$90.85	$90.80
Purchase #3	$113.40	6.359%	$120.6111	$120.61	$120.60	$120.60
Purchase #4	$125.68	12.330%	$141.1763	$141.18	$141.20	$141.20
Purchase #5	$247.55	10.515%	$273.5799	$273.58	$273.60	$273.60
Purchase #6	$73.81	6.872%	$78.8822	$78.88	$78.90	$78.90
Purchase #7	$126.34	12.825%	$142.5431	$142.54	$142.55	$142.50
7 purchase totals =	$1,019.43		$1,133.2677	$1,133.26	$1,133.35	$1,133.20