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	$165.87	7.254%	$177.9022	$177.90	$177.90	$177.90
Purchase #2	$53.86	13.746%	$61.2636	$61.26	$61.25	$61.30
Purchase #3	$99.92	9.524%	$109.4364	$109.44	$109.45	$109.40
Purchase #4	$119.43	10.865%	$132.4061	$132.41	$132.40	$132.40
Purchase #5	$127.41	9.662%	$139.7204	$139.72	$139.70	$139.70
Purchase #6	$168.98	9.828%	$185.5874	$185.59	$185.60	$185.60
Purchase #7	$112.59	8.212%	$121.8359	$121.84	$121.85	$121.80
7 purchase totals =	$848.06		$928.1520	$928.16	$928.15	$928.10