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	$138.72	8.385%	$150.3517	$150.35	$150.35	$150.40
Purchase #2	$222.50	12.712%	$250.7842	$250.78	$250.80	$250.80
Purchase #3	$59.95	9.167%	$65.4456	$65.45	$65.45	$65.40
Purchase #4	$59.87	8.437%	$64.9212	$64.92	$64.90	$64.90
Purchase #5	$65.48	13.180%	$74.1103	$74.11	$74.10	$74.10
Purchase #6	$170.80	10.402%	$188.5666	$188.57	$188.55	$188.60
Purchase #7	$37.46	4.441%	$39.1236	$39.12	$39.10	$39.10
7 purchase totals =	$754.78		$833.3032	$833.30	$833.25	$833.30