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	$33.31	9.169%	$36.3642	$36.36	$36.35	$36.40
Purchase #2	$140.42	4.371%	$146.5578	$146.56	$146.55	$146.60
Purchase #3	$125.35	13.861%	$142.7248	$142.72	$142.70	$142.70
Purchase #4	$52.62	13.539%	$59.7442	$59.74	$59.75	$59.70
Purchase #5	$61.26	9.740%	$67.2267	$67.23	$67.25	$67.20
Purchase #6	$72.95	10.725%	$80.7739	$80.77	$80.75	$80.80
Purchase #7	$135.78	7.116%	$145.4421	$145.44	$145.45	$145.40
7 purchase totals =	$621.69		$678.8337	$678.82	$678.80	$678.80