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	$234.83	4.153%	$244.5825	$244.58	$244.60	$244.60
Purchase #2	$82.90	4.480%	$86.6139	$86.61	$86.60	$86.60
Purchase #3	$62.38	7.768%	$67.2257	$67.23	$67.25	$67.20
Purchase #4	$132.73	3.576%	$137.4764	$137.48	$137.50	$137.50
Purchase #5	$6.45	12.309%	$7.2439	$7.24	$7.25	$7.20
Purchase #6	$163.89	13.693%	$186.3315	$186.33	$186.35	$186.30
Purchase #7	$165.34	13.847%	$188.2346	$188.23	$188.25	$188.20
7 purchase totals =	$848.52		$917.7085	$917.70	$917.80	$917.60