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	$46.55	10.358%	$51.3716	$51.37	$51.35	$51.40
Purchase #2	$92.69	12.560%	$104.3319	$104.33	$104.35	$104.30
Purchase #3	$29.62	9.863%	$32.5414	$32.54	$32.55	$32.50
Purchase #4	$208.29	10.250%	$229.6397	$229.64	$229.65	$229.60
Purchase #5	$22.73	6.386%	$24.1815	$24.18	$24.20	$24.20
Purchase #6	$151.90	7.165%	$162.7836	$162.78	$162.80	$162.80
Purchase #7	$40.43	11.341%	$45.0152	$45.02	$45.00	$45.00
7 purchase totals =	$592.21		$649.8649	$649.86	$649.90	$649.80