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	$44.47	11.421%	$49.5489	$49.55	$49.55	$49.50
Purchase #2	$69.48	12.599%	$78.2338	$78.23	$78.25	$78.20
Purchase #3	$149.94	12.377%	$168.4981	$168.50	$168.50	$168.50
Purchase #4	$144.69	13.381%	$164.051	$164.05	$164.05	$164.10
Purchase #5	$99.47	4.377%	$103.8238	$103.82	$103.80	$103.80
Purchase #6	$172.35	8.408%	$186.8412	$186.84	$186.85	$186.80
Purchase #7	$202.44	9.690%	$222.0564	$222.06	$222.05	$222.10
7 purchase totals =	$882.84		$973.0532	$973.05	$973.05	$973.00