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	$201.66	10.139%	$222.1063	$222.11	$222.10	$222.10
Purchase #2	$133.69	6.299%	$142.1111	$142.11	$142.10	$142.10
Purchase #3	$153.68	8.653%	$166.9779	$166.98	$167.00	$167.00
Purchase #4	$119.33	6.131%	$126.6461	$126.65	$126.65	$126.60
Purchase #5	$28.33	9.697%	$31.0772	$31.08	$31.10	$31.10
Purchase #6	$82.42	11.535%	$91.9271	$91.93	$91.95	$91.90
Purchase #7	$29.93	13.349%	$33.9254	$33.93	$33.95	$33.90
7 purchase totals =	$749.04		$814.7711	$814.79	$814.85	$814.70