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	$88.78	12.411%	$99.7985	$99.80	$99.80	$99.80
Purchase #2	$198.48	13.425%	$225.1259	$225.13	$225.15	$225.10
Purchase #3	$83.41	12.126%	$93.5243	$93.52	$93.50	$93.50
Purchase #4	$222.97	11.521%	$248.6584	$248.66	$248.65	$248.70
Purchase #5	$184.87	13.498%	$209.8238	$209.82	$209.80	$209.80
Purchase #6	$38.76	4.385%	$40.4596	$40.46	$40.45	$40.50
Purchase #7	$83.67	3.422%	$86.5332	$86.53	$86.55	$86.50
7 purchase totals =	$900.94		$1,003.9237	$1,003.92	$1,003.90	$1,003.90