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	$5.50	8.386%	$5.9612	$5.96	$5.95	$6.00
Purchase #2	$151.93	13.430%	$172.3342	$172.33	$172.35	$172.30
Purchase #3	$197.57	12.273%	$221.8178	$221.82	$221.80	$221.80
Purchase #4	$175.77	11.574%	$196.1136	$196.11	$196.10	$196.10
Purchase #5	$56.88	4.306%	$59.3293	$59.33	$59.35	$59.30
Purchase #6	$126.49	13.692%	$143.809	$143.81	$143.80	$143.80
Purchase #7	$179.64	5.695%	$189.8705	$189.87	$189.85	$189.90
7 purchase totals =	$893.78		$989.2356	$989.23	$989.20	$989.20