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	$182.69	3.121%	$188.3918	$188.39	$188.40	$188.40
Purchase #2	$80.74	7.143%	$86.5073	$86.51	$86.50	$86.50
Purchase #3	$64.90	4.843%	$68.0431	$68.04	$68.05	$68.00
Purchase #4	$40.73	4.463%	$42.5478	$42.55	$42.55	$42.50
Purchase #5	$217.38	12.211%	$243.9243	$243.92	$243.90	$243.90
Purchase #6	$28.66	3.874%	$29.7703	$29.77	$29.75	$29.80
Purchase #7	$20.79	5.153%	$21.8613	$21.86	$21.85	$21.90
7 purchase totals =	$635.89		$681.0459	$681.04	$681.00	$681.00