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	$153.80	9.427%	$168.2987	$168.30	$168.30	$168.30
Purchase #2	$219.44	6.331%	$233.3327	$233.33	$233.35	$233.30
Purchase #3	$166.66	3.702%	$172.8298	$172.83	$172.85	$172.80
Purchase #4	$55.33	9.418%	$60.541	$60.54	$60.55	$60.50
Purchase #5	$11.98	11.132%	$13.3136	$13.31	$13.30	$13.30
Purchase #6	$105.29	11.780%	$117.6932	$117.69	$117.70	$117.70
Purchase #7	$194.33	11.702%	$217.0705	$217.07	$217.05	$217.10
7 purchase totals =	$906.83		$983.0795	$983.07	$983.10	$983.00