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	$38.33	7.546%	$41.2224	$41.22	$41.20	$41.20
Purchase #2	$79.38	8.536%	$86.1559	$86.16	$86.15	$86.20
Purchase #3	$158.86	13.666%	$180.5698	$180.57	$180.55	$180.60
Purchase #4	$229.77	13.753%	$261.3703	$261.37	$261.35	$261.40
Purchase #5	$5.29	11.473%	$5.8969	$5.90	$5.90	$5.90
Purchase #6	$56.69	5.714%	$59.9293	$59.93	$59.95	$59.90
Purchase #7	$97.26	12.662%	$109.5751	$109.58	$109.60	$109.60
7 purchase totals =	$665.58		$744.7197	$744.73	$744.70	$744.80