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	$72.86	7.444%	$78.2837	$78.28	$78.30	$78.30
Purchase #2	$6.48	9.704%	$7.1088	$7.11	$7.10	$7.10
Purchase #3	$145.82	13.382%	$165.3336	$165.33	$165.35	$165.30
Purchase #4	$15.86	3.596%	$16.4303	$16.43	$16.45	$16.40
Purchase #5	$235.57	6.147%	$250.0505	$250.05	$250.05	$250.10
Purchase #6	$47.53	6.141%	$50.4488	$50.45	$50.45	$50.40
Purchase #7	$36.44	10.411%	$40.2338	$40.23	$40.25	$40.20
7 purchase totals =	$560.56		$607.8895	$607.88	$607.95	$607.80