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	$208.56	6.602%	$222.3291	$222.33	$222.35	$222.30
Purchase #2	$139.51	3.112%	$143.8516	$143.85	$143.85	$143.90
Purchase #3	$150.85	6.387%	$160.4848	$160.48	$160.50	$160.50
Purchase #4	$161.59	3.245%	$166.8336	$166.83	$166.85	$166.80
Purchase #5	$31.79	4.711%	$33.2876	$33.29	$33.30	$33.30
Purchase #6	$23.51	12.836%	$26.5277	$26.53	$26.55	$26.50
Purchase #7	$220.43	12.668%	$248.3541	$248.35	$248.35	$248.40
7 purchase totals =	$936.24		$1,001.6685	$1,001.66	$1,001.75	$1,001.70