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	$73.51	10.331%	$81.1043	$81.10	$81.10	$81.10
Purchase #2	$172.83	13.736%	$196.5699	$196.57	$196.55	$196.60
Purchase #3	$61.76	13.556%	$70.1322	$70.13	$70.15	$70.10
Purchase #4	$80.87	7.498%	$86.9336	$86.93	$86.95	$86.90
Purchase #5	$60.94	3.285%	$62.9419	$62.94	$62.95	$62.90
Purchase #6	$128.86	9.733%	$141.4019	$141.40	$141.40	$141.40
Purchase #7	$245.85	5.275%	$258.8186	$258.82	$258.80	$258.80
7 purchase totals =	$824.62		$897.9024	$897.89	$897.90	$897.80