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	$33.61	12.473%	$37.8022	$37.80	$37.80	$37.80
Purchase #2	$21.86	11.670%	$24.4111	$24.41	$24.40	$24.40
Purchase #3	$46.96	8.190%	$50.806	$50.81	$50.80	$50.80
Purchase #4	$32.55	7.848%	$35.1045	$35.10	$35.10	$35.10
Purchase #5	$24.85	13.670%	$28.247	$28.25	$28.25	$28.20
Purchase #6	$54.46	3.485%	$56.3579	$56.36	$56.35	$56.40
Purchase #7	$39.56	7.272%	$42.4368	$42.44	$42.45	$42.40
7 purchase totals =	$253.85		$275.1655	$275.17	$275.15	$275.10