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	$164.83	9.185%	$179.9696	$179.97	$179.95	$180.00
Purchase #2	$181.64	7.441%	$195.1558	$195.16	$195.15	$195.20
Purchase #3	$243.31	12.825%	$274.5145	$274.51	$274.50	$274.50
Purchase #4	$51.53	9.289%	$56.3166	$56.32	$56.30	$56.30
Purchase #5	$79.56	9.208%	$86.8859	$86.89	$86.90	$86.90
Purchase #6	$105.77	10.566%	$116.9457	$116.95	$116.95	$116.90
Purchase #7	$79.91	13.627%	$90.7993	$90.80	$90.80	$90.80
7 purchase totals =	$906.55		$1,000.5874	$1,000.60	$1,000.55	$1,000.60