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	$30.91	3.121%	$31.8747	$31.87	$31.85	$31.90
Purchase #2	$46.39	9.696%	$50.888	$50.89	$50.90	$50.90
Purchase #3	$27.51	6.341%	$29.2544	$29.25	$29.25	$29.30
Purchase #4	$166.39	13.317%	$188.5482	$188.55	$188.55	$188.50
Purchase #5	$62.80	6.763%	$67.0472	$67.05	$67.05	$67.00
Purchase #6	$24.38	11.801%	$27.2571	$27.26	$27.25	$27.30
Purchase #7	$51.69	11.154%	$57.4555	$57.46	$57.45	$57.50
7 purchase totals =	$410.07		$452.3251	$452.33	$452.30	$452.40