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	$94.58	6.252%	$100.4931	$100.49	$100.50	$100.50
Purchase #2	$53.53	7.469%	$57.5282	$57.53	$57.55	$57.50
Purchase #3	$51.27	13.617%	$58.2514	$58.25	$58.25	$58.30
Purchase #4	$201.34	12.546%	$226.6001	$226.60	$226.60	$226.60
Purchase #5	$241.73	13.179%	$273.5876	$273.59	$273.60	$273.60
Purchase #6	$197.49	6.573%	$210.471	$210.47	$210.45	$210.50
Purchase #7	$148.30	5.408%	$156.3201	$156.32	$156.30	$156.30
7 purchase totals =	$988.24		$1,083.2515	$1,083.25	$1,083.25	$1,083.30