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	$39.48	6.759%	$42.1485	$42.15	$42.15	$42.10
Purchase #2	$204.57	10.830%	$226.7249	$226.72	$226.70	$226.70
Purchase #3	$145.80	4.865%	$152.8932	$152.89	$152.90	$152.90
Purchase #4	$246.61	4.390%	$257.4362	$257.44	$257.45	$257.40
Purchase #5	$216.77	3.606%	$224.5867	$224.59	$224.60	$224.60
Purchase #6	$88.28	6.481%	$94.0014	$94.00	$94.00	$94.00
Purchase #7	$62.93	7.658%	$67.7492	$67.75	$67.75	$67.70
7 purchase totals =	$1,004.44		$1,065.5401	$1,065.54	$1,065.55	$1,065.40