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	$40.91	8.323%	$44.3149	$44.31	$44.30	$44.30
Purchase #2	$57.32	12.692%	$64.5951	$64.60	$64.60	$64.60
Purchase #3	$216.51	3.604%	$224.313	$224.31	$224.30	$224.30
Purchase #4	$186.69	7.420%	$200.5424	$200.54	$200.55	$200.50
Purchase #5	$121.54	12.294%	$136.4821	$136.48	$136.50	$136.50
Purchase #6	$169.45	10.165%	$186.6746	$186.67	$186.65	$186.70
Purchase #7	$65.71	8.679%	$71.413	$71.41	$71.40	$71.40
7 purchase totals =	$858.13		$928.3351	$928.32	$928.30	$928.30