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	$92.36	13.230%	$104.5792	$104.58	$104.60	$104.60
Purchase #2	$36.80	5.686%	$38.8924	$38.89	$38.90	$38.90
Purchase #3	$78.30	5.610%	$82.6926	$82.69	$82.70	$82.70
Purchase #4	$242.99	3.421%	$251.3027	$251.30	$251.30	$251.30
Purchase #5	$83.94	8.142%	$90.7744	$90.77	$90.75	$90.80
Purchase #6	$167.31	13.782%	$190.3687	$190.37	$190.35	$190.40
Purchase #7	$149.25	4.775%	$156.3767	$156.38	$156.40	$156.40
7 purchase totals =	$850.95		$914.9867	$914.98	$915.00	$915.10