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	$199.98	6.679%	$213.3367	$213.34	$213.35	$213.30
Purchase #2	$18.43	12.682%	$20.7673	$20.77	$20.75	$20.80
Purchase #3	$231.77	8.249%	$250.8887	$250.89	$250.90	$250.90
Purchase #4	$32.59	3.646%	$33.7782	$33.78	$33.80	$33.80
Purchase #5	$49.87	10.586%	$55.1492	$55.15	$55.15	$55.10
Purchase #6	$55.46	6.550%	$59.0926	$59.09	$59.10	$59.10
Purchase #7	$219.99	11.116%	$244.4441	$244.44	$244.45	$244.40
7 purchase totals =	$808.09		$877.4568	$877.46	$877.50	$877.40