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	$141.25	12.677%	$159.1563	$159.16	$159.15	$159.20
Purchase #2	$188.57	12.133%	$211.4492	$211.45	$211.45	$211.40
Purchase #3	$114.90	7.680%	$123.7243	$123.72	$123.70	$123.70
Purchase #4	$162.75	7.208%	$174.481	$174.48	$174.50	$174.50
Purchase #5	$13.27	12.379%	$14.9127	$14.91	$14.90	$14.90
Purchase #6	$40.95	10.175%	$45.1167	$45.12	$45.10	$45.10
Purchase #7	$101.25	8.104%	$109.4553	$109.46	$109.45	$109.50
7 purchase totals =	$762.94		$838.2955	$838.30	$838.25	$838.30