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	$33.90	13.353%	$38.4267	$38.43	$38.45	$38.40
Purchase #2	$45.89	3.316%	$47.4117	$47.41	$47.40	$47.40
Purchase #3	$241.44	10.808%	$267.5348	$267.53	$267.55	$267.50
Purchase #4	$57.63	13.354%	$65.3259	$65.33	$65.35	$65.30
Purchase #5	$213.66	10.263%	$235.5879	$235.59	$235.60	$235.60
Purchase #6	$73.45	13.803%	$83.5883	$83.59	$83.60	$83.60
Purchase #7	$232.65	13.796%	$264.7464	$264.75	$264.75	$264.70
7 purchase totals =	$898.62		$1,002.6217	$1,002.63	$1,002.70	$1,002.50