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	$85.48	5.222%	$89.9438	$89.94	$89.95	$89.90
Purchase #2	$105.65	3.735%	$109.596	$109.60	$109.60	$109.60
Purchase #3	$216.40	7.314%	$232.2275	$232.23	$232.25	$232.20
Purchase #4	$130.94	4.129%	$136.3465	$136.35	$136.35	$136.30
Purchase #5	$194.31	8.398%	$210.6282	$210.63	$210.65	$210.60
Purchase #6	$126.25	13.726%	$143.5791	$143.58	$143.60	$143.60
Purchase #7	$246.92	11.102%	$274.3331	$274.33	$274.35	$274.30
7 purchase totals =	$1,105.95		$1,196.6542	$1,196.66	$1,196.75	$1,196.50