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	$172.94	5.139%	$181.8274	$181.83	$181.85	$181.80
Purchase #2	$196.53	8.523%	$213.2803	$213.28	$213.30	$213.30
Purchase #3	$65.58	6.405%	$69.7804	$69.78	$69.80	$69.80
Purchase #4	$242.81	12.493%	$273.1443	$273.14	$273.15	$273.10
Purchase #5	$39.50	13.645%	$44.8898	$44.89	$44.90	$44.90
Purchase #6	$42.64	7.164%	$45.6947	$45.69	$45.70	$45.70
Purchase #7	$217.25	9.601%	$238.1082	$238.11	$238.10	$238.10
7 purchase totals =	$977.25		$1,066.7251	$1,066.72	$1,066.80	$1,066.70