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	$81.71	10.202%	$90.0461	$90.05	$90.05	$90.00
Purchase #2	$42.76	9.114%	$46.6571	$46.66	$46.65	$46.70
Purchase #3	$97.57	8.573%	$105.9347	$105.93	$105.95	$105.90
Purchase #4	$42.78	3.654%	$44.3432	$44.34	$44.35	$44.30
Purchase #5	$129.90	11.730%	$145.1373	$145.14	$145.15	$145.10
Purchase #6	$167.68	10.345%	$185.0265	$185.03	$185.05	$185.00
Purchase #7	$13.46	13.159%	$15.2312	$15.23	$15.25	$15.20
7 purchase totals =	$575.86		$632.3761	$632.38	$632.45	$632.20