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	$150.29	9.612%	$164.7359	$164.74	$164.75	$164.70
Purchase #2	$217.97	5.298%	$229.5181	$229.52	$229.50	$229.50
Purchase #3	$148.70	10.590%	$164.4473	$164.45	$164.45	$164.40
Purchase #4	$34.31	6.584%	$36.569	$36.57	$36.55	$36.60
Purchase #5	$208.76	11.399%	$232.5566	$232.56	$232.55	$232.60
Purchase #6	$97.27	4.761%	$101.901	$101.90	$101.90	$101.90
Purchase #7	$157.37	8.708%	$171.0738	$171.07	$171.05	$171.10
7 purchase totals =	$1,014.67		$1,100.8017	$1,100.81	$1,100.75	$1,100.80