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	$36.88	8.468%	$40.003	$40.00	$40.00	$40.00
Purchase #2	$51.90	10.507%	$57.3531	$57.35	$57.35	$57.40
Purchase #3	$188.54	4.143%	$196.3512	$196.35	$196.35	$196.40
Purchase #4	$128.49	10.674%	$142.205	$142.21	$142.20	$142.20
Purchase #5	$30.80	6.871%	$32.9163	$32.92	$32.90	$32.90
Purchase #6	$250.78	10.204%	$276.3696	$276.37	$276.35	$276.40
Purchase #7	$41.99	7.568%	$45.1678	$45.17	$45.15	$45.20
7 purchase totals =	$729.38		$790.3660	$790.37	$790.30	$790.50