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	$30.73	5.365%	$32.3787	$32.38	$32.40	$32.40
Purchase #2	$247.46	12.161%	$277.5536	$277.55	$277.55	$277.60
Purchase #3	$184.76	6.295%	$196.3906	$196.39	$196.40	$196.40
Purchase #4	$173.80	5.517%	$183.3885	$183.39	$183.40	$183.40
Purchase #5	$82.78	6.136%	$87.8594	$87.86	$87.85	$87.90
Purchase #6	$146.43	5.400%	$154.3372	$154.34	$154.35	$154.30
Purchase #7	$183.90	13.319%	$208.3936	$208.39	$208.40	$208.40
7 purchase totals =	$1,049.86		$1,140.3016	$1,140.30	$1,140.35	$1,140.40