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	$116.70	11.666%	$130.3142	$130.31	$130.30	$130.30
Purchase #2	$45.63	4.309%	$47.5962	$47.60	$47.60	$47.60
Purchase #3	$126.60	7.582%	$136.1988	$136.20	$136.20	$136.20
Purchase #4	$67.45	13.397%	$76.4863	$76.49	$76.50	$76.50
Purchase #5	$207.78	10.425%	$229.4411	$229.44	$229.45	$229.40
Purchase #6	$55.64	7.535%	$59.8325	$59.83	$59.85	$59.80
Purchase #7	$151.73	7.317%	$162.8321	$162.83	$162.85	$162.80
7 purchase totals =	$771.53		$842.7012	$842.70	$842.75	$842.60