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	$28.36	13.479%	$32.1826	$32.18	$32.20	$32.20
Purchase #2	$72.28	13.184%	$81.8094	$81.81	$81.80	$81.80
Purchase #3	$105.80	8.639%	$114.9401	$114.94	$114.95	$114.90
Purchase #4	$78.59	13.182%	$88.9497	$88.95	$88.95	$88.90
Purchase #5	$93.86	9.774%	$103.0339	$103.03	$103.05	$103.00
Purchase #6	$173.56	6.644%	$185.0913	$185.09	$185.10	$185.10
Purchase #7	$55.66	8.661%	$60.4807	$60.48	$60.50	$60.50
7 purchase totals =	$608.11		$666.4877	$666.48	$666.55	$666.40