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	$225.27	7.452%	$242.0571	$242.06	$242.05	$242.10
Purchase #2	$248.52	9.854%	$273.0092	$273.01	$273.00	$273.00
Purchase #3	$19.28	11.735%	$21.5425	$21.54	$21.55	$21.50
Purchase #4	$54.26	12.196%	$60.8775	$60.88	$60.90	$60.90
Purchase #5	$17.57	3.103%	$18.1152	$18.12	$18.10	$18.10
Purchase #6	$219.76	11.860%	$245.8235	$245.82	$245.80	$245.80
Purchase #7	$153.79	10.601%	$170.0933	$170.09	$170.10	$170.10
7 purchase totals =	$938.45		$1,031.5183	$1,031.52	$1,031.50	$1,031.50