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	$36.85	3.788%	$38.2459	$38.25	$38.25	$38.20
Purchase #2	$173.41	9.533%	$189.9412	$189.94	$189.95	$189.90
Purchase #3	$37.97	12.317%	$42.6468	$42.65	$42.65	$42.60
Purchase #4	$246.51	4.221%	$256.9152	$256.92	$256.90	$256.90
Purchase #5	$237.98	11.246%	$264.7432	$264.74	$264.75	$264.70
Purchase #6	$40.58	4.669%	$42.4747	$42.47	$42.45	$42.50
Purchase #7	$111.62	13.207%	$126.3617	$126.36	$126.35	$126.40
7 purchase totals =	$884.92		$961.3287	$961.33	$961.30	$961.20