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	$63.27	13.231%	$71.6413	$71.64	$71.65	$71.60
Purchase #2	$241.66	13.159%	$273.46	$273.46	$273.45	$273.50
Purchase #3	$239.49	6.809%	$255.7969	$255.80	$255.80	$255.80
Purchase #4	$207.74	3.763%	$215.5573	$215.56	$215.55	$215.60
Purchase #5	$26.69	7.624%	$28.7248	$28.72	$28.70	$28.70
Purchase #6	$56.44	5.274%	$59.4166	$59.42	$59.40	$59.40
Purchase #7	$91.48	13.600%	$103.9213	$103.92	$103.90	$103.90
7 purchase totals =	$926.77		$1,008.5182	$1,008.52	$1,008.45	$1,008.50