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	$187.61	4.772%	$196.5627	$196.56	$196.55	$196.60
Purchase #2	$182.80	9.827%	$200.7638	$200.76	$200.75	$200.80
Purchase #3	$33.44	10.765%	$37.0398	$37.04	$37.05	$37.00
Purchase #4	$133.80	4.791%	$140.2104	$140.21	$140.20	$140.20
Purchase #5	$97.46	8.612%	$105.8533	$105.85	$105.85	$105.90
Purchase #6	$96.95	12.165%	$108.744	$108.74	$108.75	$108.70
Purchase #7	$44.64	13.716%	$50.7628	$50.76	$50.75	$50.80
7 purchase totals =	$776.70		$839.9368	$839.92	$839.90	$840.00