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	$133.84	5.192%	$140.789	$140.79	$140.80	$140.80
Purchase #2	$196.73	13.109%	$222.5193	$222.52	$222.50	$222.50
Purchase #3	$81.98	7.759%	$88.3408	$88.34	$88.35	$88.30
Purchase #4	$222.64	11.767%	$248.838	$248.84	$248.85	$248.80
Purchase #5	$131.57	10.647%	$145.5783	$145.58	$145.60	$145.60
Purchase #6	$99.60	12.732%	$112.2811	$112.28	$112.30	$112.30
Purchase #7	$54.65	5.210%	$57.4973	$57.50	$57.50	$57.50
7 purchase totals =	$921.01		$1,015.8438	$1,015.85	$1,015.90	$1,015.80