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	$30.35	9.177%	$33.1352	$33.14	$33.15	$33.10
Purchase #2	$82.47	3.484%	$85.3433	$85.34	$85.35	$85.30
Purchase #3	$135.64	4.610%	$141.893	$141.89	$141.90	$141.90
Purchase #4	$218.59	6.639%	$233.1022	$233.10	$233.10	$233.10
Purchase #5	$77.25	3.182%	$79.7081	$79.71	$79.70	$79.70
Purchase #6	$173.86	11.277%	$193.4662	$193.47	$193.45	$193.50
Purchase #7	$51.44	12.470%	$57.8546	$57.85	$57.85	$57.90
7 purchase totals =	$769.60		$824.5026	$824.50	$824.50	$824.50