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	$34.25	9.564%	$37.5257	$37.53	$37.55	$37.50
Purchase #2	$30.98	5.843%	$32.7902	$32.79	$32.80	$32.80
Purchase #3	$126.50	3.379%	$130.7744	$130.77	$130.75	$130.80
Purchase #4	$126.95	8.237%	$137.4069	$137.41	$137.40	$137.40
Purchase #5	$213.31	12.292%	$239.5301	$239.53	$239.55	$239.50
Purchase #6	$200.81	4.212%	$209.2681	$209.27	$209.25	$209.30
Purchase #7	$198.74	9.773%	$218.1629	$218.16	$218.15	$218.20
7 purchase totals =	$931.54		$1,005.4583	$1,005.46	$1,005.45	$1,005.50