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	$38.79	5.414%	$40.8901	$40.89	$40.90	$40.90
Purchase #2	$133.73	5.641%	$141.2737	$141.27	$141.25	$141.30
Purchase #3	$146.62	12.472%	$164.9064	$164.91	$164.90	$164.90
Purchase #4	$59.89	11.683%	$66.8869	$66.89	$66.90	$66.90
Purchase #5	$57.86	3.867%	$60.0974	$60.10	$60.10	$60.10
Purchase #6	$209.85	5.781%	$221.9814	$221.98	$222.00	$222.00
Purchase #7	$51.74	10.659%	$57.255	$57.26	$57.25	$57.30
7 purchase totals =	$698.48		$753.2909	$753.30	$753.30	$753.40