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	$21.63	11.828%	$24.1884	$24.19	$24.20	$24.20
Purchase #2	$67.67	9.125%	$73.8449	$73.84	$73.85	$73.80
Purchase #3	$105.72	3.475%	$109.3938	$109.39	$109.40	$109.40
Purchase #4	$145.82	3.578%	$151.0374	$151.04	$151.05	$151.00
Purchase #5	$203.30	3.603%	$210.6249	$210.62	$210.60	$210.60
Purchase #6	$150.45	6.370%	$160.0337	$160.03	$160.05	$160.00
Purchase #7	$249.46	9.679%	$273.6052	$273.61	$273.60	$273.60
7 purchase totals =	$944.05		$1,002.7283	$1,002.72	$1,002.75	$1,002.60