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	$63.47	12.499%	$71.4031	$71.40	$71.40	$71.40
Purchase #2	$226.67	10.485%	$250.4363	$250.44	$250.45	$250.40
Purchase #3	$124.93	13.709%	$142.0567	$142.06	$142.05	$142.10
Purchase #4	$137.38	6.484%	$146.2877	$146.29	$146.30	$146.30
Purchase #5	$146.68	8.821%	$159.6186	$159.62	$159.60	$159.60
Purchase #6	$84.34	7.228%	$90.4361	$90.44	$90.45	$90.40
Purchase #7	$139.34	12.539%	$156.8118	$156.81	$156.80	$156.80
7 purchase totals =	$922.81		$1,017.0503	$1,017.06	$1,017.05	$1,017.00