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	$103.69	8.869%	$112.8863	$112.89	$112.90	$112.90
Purchase #2	$51.98	4.796%	$54.473	$54.47	$54.45	$54.50
Purchase #3	$33.89	4.538%	$35.4279	$35.43	$35.45	$35.40
Purchase #4	$134.84	8.735%	$146.6183	$146.62	$146.60	$146.60
Purchase #5	$106.57	7.721%	$114.7983	$114.80	$114.80	$114.80
Purchase #6	$169.45	10.841%	$187.8201	$187.82	$187.80	$187.80
Purchase #7	$82.50	5.324%	$86.8923	$86.89	$86.90	$86.90
7 purchase totals =	$682.92		$738.9162	$738.92	$738.90	$738.90