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	$167.37	12.403%	$188.1289	$188.13	$188.15	$188.10
Purchase #2	$170.60	8.734%	$185.5002	$185.50	$185.50	$185.50
Purchase #3	$45.51	13.713%	$51.7508	$51.75	$51.75	$51.80
Purchase #4	$248.61	9.567%	$272.3945	$272.39	$272.40	$272.40
Purchase #5	$53.96	6.435%	$57.4323	$57.43	$57.45	$57.40
Purchase #6	$178.95	6.859%	$191.2242	$191.22	$191.20	$191.20
Purchase #7	$65.79	12.187%	$73.8078	$73.81	$73.80	$73.80
7 purchase totals =	$930.79		$1,020.2387	$1,020.23	$1,020.25	$1,020.20