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	$27.53	5.627%	$29.0791	$29.08	$29.10	$29.10
Purchase #2	$161.71	4.284%	$168.6377	$168.64	$168.65	$168.60
Purchase #3	$200.76	7.708%	$216.2346	$216.23	$216.25	$216.20
Purchase #4	$52.46	4.874%	$55.0169	$55.02	$55.00	$55.00
Purchase #5	$86.75	3.817%	$90.0612	$90.06	$90.05	$90.10
Purchase #6	$192.26	10.229%	$211.9263	$211.93	$211.95	$211.90
Purchase #7	$33.25	12.743%	$37.487	$37.49	$37.50	$37.50
7 purchase totals =	$754.72		$808.4428	$808.45	$808.50	$808.40