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	$82.61	3.770%	$85.7244	$85.72	$85.70	$85.70
Purchase #2	$184.36	12.490%	$207.3866	$207.39	$207.40	$207.40
Purchase #3	$82.39	9.395%	$90.1305	$90.13	$90.15	$90.10
Purchase #4	$157.67	10.318%	$173.9384	$173.94	$173.95	$173.90
Purchase #5	$25.73	7.419%	$27.6389	$27.64	$27.65	$27.60
Purchase #6	$61.77	13.129%	$69.8798	$69.88	$69.90	$69.90
Purchase #7	$48.36	8.515%	$52.4779	$52.48	$52.50	$52.50
7 purchase totals =	$642.89		$707.1765	$707.18	$707.25	$707.10