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	$126.46	7.694%	$136.1898	$136.19	$136.20	$136.20
Purchase #2	$41.27	11.140%	$45.8675	$45.87	$45.85	$45.90
Purchase #3	$108.31	10.621%	$119.8136	$119.81	$119.80	$119.80
Purchase #4	$112.33	4.461%	$117.341	$117.34	$117.35	$117.30
Purchase #5	$20.56	7.731%	$22.1495	$22.15	$22.15	$22.10
Purchase #6	$97.57	12.190%	$109.4638	$109.46	$109.45	$109.50
Purchase #7	$156.29	5.393%	$164.7187	$164.72	$164.70	$164.70
7 purchase totals =	$662.79		$715.5439	$715.54	$715.50	$715.50