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	$64.94	6.151%	$68.9345	$68.93	$68.95	$68.90
Purchase #2	$215.64	7.259%	$231.2933	$231.29	$231.30	$231.30
Purchase #3	$235.82	13.144%	$266.8162	$266.82	$266.80	$266.80
Purchase #4	$54.88	8.119%	$59.3357	$59.34	$59.35	$59.30
Purchase #5	$242.85	8.864%	$264.3762	$264.38	$264.40	$264.40
Purchase #6	$30.66	8.135%	$33.1542	$33.15	$33.15	$33.20
Purchase #7	$185.30	8.229%	$200.5483	$200.55	$200.55	$200.50
7 purchase totals =	$1,030.09		$1,124.4584	$1,124.46	$1,124.50	$1,124.40