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	$165.39	8.806%	$179.9542	$179.95	$179.95	$180.00
Purchase #2	$240.76	13.459%	$273.1639	$273.16	$273.15	$273.20
Purchase #3	$196.59	7.165%	$210.6757	$210.68	$210.70	$210.70
Purchase #4	$77.59	5.385%	$81.7682	$81.77	$81.75	$81.80
Purchase #5	$135.45	8.299%	$146.691	$146.69	$146.70	$146.70
Purchase #6	$52.94	5.554%	$55.8803	$55.88	$55.90	$55.90
Purchase #7	$128.98	6.472%	$137.3276	$137.33	$137.35	$137.30
7 purchase totals =	$997.70		$1,085.4609	$1,085.46	$1,085.50	$1,085.60