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	$142.77	10.295%	$157.4682	$157.47	$157.45	$157.50
Purchase #2	$97.61	7.682%	$105.1084	$105.11	$105.10	$105.10
Purchase #3	$129.65	6.281%	$137.7933	$137.79	$137.80	$137.80
Purchase #4	$161.73	5.757%	$171.0408	$171.04	$171.05	$171.00
Purchase #5	$53.38	11.566%	$59.5539	$59.55	$59.55	$59.60
Purchase #6	$226.83	11.757%	$253.4984	$253.50	$253.50	$253.50
Purchase #7	$217.98	12.165%	$244.4973	$244.50	$244.50	$244.50
7 purchase totals =	$1,029.95		$1,128.9603	$1,128.96	$1,128.95	$1,129.00