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	$105.89	13.678%	$120.3736	$120.37	$120.35	$120.40
Purchase #2	$152.44	12.265%	$171.1368	$171.14	$171.15	$171.10
Purchase #3	$41.68	6.284%	$44.2992	$44.30	$44.30	$44.30
Purchase #4	$203.95	12.693%	$229.8374	$229.84	$229.85	$229.80
Purchase #5	$210.57	6.287%	$223.8085	$223.81	$223.80	$223.80
Purchase #6	$101.81	10.544%	$112.5448	$112.54	$112.55	$112.50
Purchase #7	$224.25	7.791%	$241.7213	$241.72	$241.70	$241.70
7 purchase totals =	$1,040.59		$1,143.7216	$1,143.72	$1,143.70	$1,143.60