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	$37.78	5.671%	$39.9225	$39.92	$39.90	$39.90
Purchase #2	$27.34	9.147%	$29.8408	$29.84	$29.85	$29.80
Purchase #3	$27.53	3.696%	$28.5475	$28.55	$28.55	$28.50
Purchase #4	$179.40	6.730%	$191.4736	$191.47	$191.45	$191.50
Purchase #5	$196.34	10.331%	$216.6239	$216.62	$216.60	$216.60
Purchase #6	$57.78	13.243%	$65.4318	$65.43	$65.45	$65.40
Purchase #7	$233.96	13.256%	$264.9737	$264.97	$264.95	$265.00
7 purchase totals =	$760.13		$836.8138	$836.80	$836.75	$836.70