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	$55.34	10.802%	$61.3178	$61.32	$61.30	$61.30
Purchase #2	$77.51	12.758%	$87.3987	$87.40	$87.40	$87.40
Purchase #3	$99.72	8.694%	$108.3897	$108.39	$108.40	$108.40
Purchase #4	$169.93	8.596%	$184.5372	$184.54	$184.55	$184.50
Purchase #5	$249.27	7.468%	$267.8855	$267.89	$267.90	$267.90
Purchase #6	$78.92	11.835%	$88.2602	$88.26	$88.25	$88.30
Purchase #7	$38.33	11.185%	$42.6172	$42.62	$42.60	$42.60
7 purchase totals =	$769.02		$840.4063	$840.42	$840.40	$840.40