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	$179.71	13.504%	$203.978	$203.98	$204.00	$204.00
Purchase #2	$145.38	11.864%	$162.6279	$162.63	$162.65	$162.60
Purchase #3	$87.75	3.709%	$91.0046	$91.00	$91.00	$91.00
Purchase #4	$150.37	3.185%	$155.1593	$155.16	$155.15	$155.20
Purchase #5	$81.53	11.160%	$90.6287	$90.63	$90.65	$90.60
Purchase #6	$45.38	12.165%	$50.9005	$50.90	$50.90	$50.90
Purchase #7	$206.99	12.640%	$233.1535	$233.15	$233.15	$233.20
7 purchase totals =	$897.11		$987.4525	$987.45	$987.50	$987.50