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	$13.55	9.588%	$14.8492	$14.85	$14.85	$14.80
Purchase #2	$123.66	11.510%	$137.8933	$137.89	$137.90	$137.90
Purchase #3	$78.44	5.112%	$82.4499	$82.45	$82.45	$82.40
Purchase #4	$235.76	7.517%	$253.4821	$253.48	$253.50	$253.50
Purchase #5	$169.45	6.172%	$179.9085	$179.91	$179.90	$179.90
Purchase #6	$157.92	10.816%	$175.0006	$175.00	$175.00	$175.00
Purchase #7	$99.53	9.267%	$108.7534	$108.75	$108.75	$108.80
7 purchase totals =	$878.31		$952.3370	$952.33	$952.35	$952.30