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	$69.25	13.280%	$78.4464	$78.45	$78.45	$78.40
Purchase #2	$202.89	8.824%	$220.793	$220.79	$220.80	$220.80
Purchase #3	$90.33	9.401%	$98.8219	$98.82	$98.80	$98.80
Purchase #4	$198.71	3.103%	$204.876	$204.88	$204.90	$204.90
Purchase #5	$123.77	3.185%	$127.7121	$127.71	$127.70	$127.70
Purchase #6	$22.35	12.738%	$25.1969	$25.20	$25.20	$25.20
Purchase #7	$192.73	9.392%	$210.8312	$210.83	$210.85	$210.80
7 purchase totals =	$900.03		$966.6775	$966.68	$966.70	$966.60