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	$36.57	13.485%	$41.5015	$41.50	$41.50	$41.50
Purchase #2	$209.77	9.425%	$229.5408	$229.54	$229.55	$229.50
Purchase #3	$52.66	9.585%	$57.7075	$57.71	$57.70	$57.70
Purchase #4	$146.48	4.398%	$152.9222	$152.92	$152.90	$152.90
Purchase #5	$40.38	6.388%	$42.9595	$42.96	$42.95	$43.00
Purchase #6	$78.81	5.863%	$83.4306	$83.43	$83.45	$83.40
Purchase #7	$121.59	8.297%	$131.6783	$131.68	$131.70	$131.70
7 purchase totals =	$686.26		$739.7404	$739.74	$739.75	$739.70