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	$81.72	11.775%	$91.3425	$91.34	$91.35	$91.30
Purchase #2	$57.53	6.716%	$61.3937	$61.39	$61.40	$61.40
Purchase #3	$26.79	8.612%	$29.0972	$29.10	$29.10	$29.10
Purchase #4	$42.31	10.518%	$46.7602	$46.76	$46.75	$46.80
Purchase #5	$196.36	13.645%	$223.1533	$223.15	$223.15	$223.20
Purchase #6	$147.31	5.485%	$155.39	$155.39	$155.40	$155.40
Purchase #7	$12.69	3.211%	$13.0975	$13.10	$13.10	$13.10
7 purchase totals =	$564.71		$620.2344	$620.23	$620.25	$620.30