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	$88.61	9.830%	$97.3204	$97.32	$97.30	$97.30
Purchase #2	$182.75	4.598%	$191.1528	$191.15	$191.15	$191.20
Purchase #3	$101.50	6.409%	$108.0051	$108.01	$108.00	$108.00
Purchase #4	$162.86	11.760%	$182.0123	$182.01	$182.00	$182.00
Purchase #5	$19.72	9.127%	$21.5198	$21.52	$21.50	$21.50
Purchase #6	$6.94	7.704%	$7.4747	$7.47	$7.45	$7.50
Purchase #7	$109.89	8.445%	$119.1702	$119.17	$119.15	$119.20
7 purchase totals =	$672.27		$726.6553	$726.65	$726.55	$726.70