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	$57.92	12.317%	$65.054	$65.05	$65.05	$65.10
Purchase #2	$129.88	7.254%	$139.3015	$139.30	$139.30	$139.30
Purchase #3	$91.57	12.227%	$102.7663	$102.77	$102.75	$102.80
Purchase #4	$47.48	13.549%	$53.9131	$53.91	$53.90	$53.90
Purchase #5	$223.58	6.691%	$238.5397	$238.54	$238.55	$238.50
Purchase #6	$102.92	9.728%	$112.9321	$112.93	$112.95	$112.90
Purchase #7	$139.73	12.333%	$156.9629	$156.96	$156.95	$157.00
7 purchase totals =	$793.08		$869.4696	$869.46	$869.45	$869.50