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	$231.55	6.378%	$246.3183	$246.32	$246.30	$246.30
Purchase #2	$99.71	6.802%	$106.4923	$106.49	$106.50	$106.50
Purchase #3	$222.47	7.819%	$239.8649	$239.86	$239.85	$239.90
Purchase #4	$169.54	3.456%	$175.3993	$175.40	$175.40	$175.40
Purchase #5	$31.29	3.808%	$32.4815	$32.48	$32.50	$32.50
Purchase #6	$55.87	12.409%	$62.8029	$62.80	$62.80	$62.80
Purchase #7	$136.99	11.333%	$152.5151	$152.52	$152.50	$152.50
7 purchase totals =	$947.42		$1,015.8743	$1,015.87	$1,015.85	$1,015.90