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	$27.34	3.680%	$28.3461	$28.35	$28.35	$28.30
Purchase #2	$52.84	4.738%	$55.3436	$55.34	$55.35	$55.30
Purchase #3	$143.88	7.188%	$154.2221	$154.22	$154.20	$154.20
Purchase #4	$109.90	7.777%	$118.4469	$118.45	$118.45	$118.40
Purchase #5	$38.44	12.127%	$43.1016	$43.10	$43.10	$43.10
Purchase #6	$101.98	8.119%	$110.2598	$110.26	$110.25	$110.30
Purchase #7	$76.58	11.220%	$85.1723	$85.17	$85.15	$85.20
7 purchase totals =	$550.96		$594.8924	$594.89	$594.85	$594.80