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	$111.78	13.160%	$126.4902	$126.49	$126.50	$126.50
Purchase #2	$127.61	9.658%	$139.9346	$139.93	$139.95	$139.90
Purchase #3	$189.67	7.499%	$203.8934	$203.89	$203.90	$203.90
Purchase #4	$67.57	9.532%	$74.0108	$74.01	$74.00	$74.00
Purchase #5	$112.45	3.583%	$116.4791	$116.48	$116.50	$116.50
Purchase #6	$166.77	11.356%	$185.7084	$185.71	$185.70	$185.70
Purchase #7	$232.92	12.459%	$261.9395	$261.94	$261.95	$261.90
7 purchase totals =	$1,008.77		$1,108.4560	$1,108.45	$1,108.50	$1,108.40