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	$178.31	5.586%	$188.2704	$188.27	$188.25	$188.30
Purchase #2	$76.73	6.211%	$81.4957	$81.50	$81.50	$81.50
Purchase #3	$74.61	8.781%	$81.1615	$81.16	$81.15	$81.20
Purchase #4	$109.48	13.129%	$123.8536	$123.85	$123.85	$123.90
Purchase #5	$13.59	5.145%	$14.2892	$14.29	$14.30	$14.30
Purchase #6	$206.48	4.367%	$215.497	$215.50	$215.50	$215.50
Purchase #7	$80.90	13.464%	$91.7924	$91.79	$91.80	$91.80
7 purchase totals =	$740.10		$796.3598	$796.36	$796.35	$796.50