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	$234.39	10.269%	$258.4595	$258.46	$258.45	$258.50
Purchase #2	$222.93	12.375%	$250.5176	$250.52	$250.50	$250.50
Purchase #3	$167.30	4.517%	$174.8569	$174.86	$174.85	$174.90
Purchase #4	$111.97	7.801%	$120.7048	$120.70	$120.70	$120.70
Purchase #5	$128.62	8.188%	$139.1514	$139.15	$139.15	$139.20
Purchase #6	$79.32	5.328%	$83.5462	$83.55	$83.55	$83.50
Purchase #7	$11.71	12.547%	$13.1793	$13.18	$13.20	$13.20
7 purchase totals =	$956.24		$1,040.4157	$1,040.42	$1,040.40	$1,040.50