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	$47.83	13.314%	$54.1981	$54.20	$54.20	$54.20
Purchase #2	$14.77	4.443%	$15.4262	$15.43	$15.45	$15.40
Purchase #3	$143.88	8.740%	$156.4551	$156.46	$156.45	$156.50
Purchase #4	$53.56	7.320%	$57.4806	$57.48	$57.50	$57.50
Purchase #5	$208.53	6.841%	$222.7955	$222.80	$222.80	$222.80
Purchase #6	$79.33	8.245%	$85.8708	$85.87	$85.85	$85.90
Purchase #7	$37.38	9.420%	$40.9012	$40.90	$40.90	$40.90
7 purchase totals =	$585.28		$633.1275	$633.14	$633.15	$633.20