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	$41.70	13.292%	$47.2428	$47.24	$47.25	$47.20
Purchase #2	$63.54	13.195%	$71.9241	$71.92	$71.90	$71.90
Purchase #3	$205.71	11.738%	$229.8562	$229.86	$229.85	$229.90
Purchase #4	$76.92	7.715%	$82.8544	$82.85	$82.85	$82.90
Purchase #5	$193.46	11.573%	$215.8491	$215.85	$215.85	$215.80
Purchase #6	$105.53	10.284%	$116.3827	$116.38	$116.40	$116.40
Purchase #7	$207.70	13.503%	$235.7457	$235.75	$235.75	$235.70
7 purchase totals =	$894.56		$999.8550	$999.85	$999.85	$999.80