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	$124.64	5.797%	$131.8654	$131.87	$131.85	$131.90
Purchase #2	$50.74	4.308%	$52.9259	$52.93	$52.95	$52.90
Purchase #3	$188.70	11.246%	$209.9212	$209.92	$209.90	$209.90
Purchase #4	$216.66	11.783%	$242.189	$242.19	$242.20	$242.20
Purchase #5	$27.51	9.705%	$30.1798	$30.18	$30.20	$30.20
Purchase #6	$126.55	11.588%	$141.2146	$141.21	$141.20	$141.20
Purchase #7	$53.85	10.668%	$59.5947	$59.59	$59.60	$59.60
7 purchase totals =	$788.65		$867.8906	$867.89	$867.90	$867.90