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	$120.60	11.392%	$134.3388	$134.34	$134.35	$134.30
Purchase #2	$215.85	10.678%	$238.8985	$238.90	$238.90	$238.90
Purchase #3	$96.50	5.115%	$101.436	$101.44	$101.45	$101.40
Purchase #4	$83.69	12.868%	$94.4592	$94.46	$94.45	$94.50
Purchase #5	$177.82	10.269%	$196.0803	$196.08	$196.10	$196.10
Purchase #6	$38.29	9.275%	$41.8414	$41.84	$41.85	$41.80
Purchase #7	$164.33	13.132%	$185.9098	$185.91	$185.90	$185.90
7 purchase totals =	$897.08		$992.9640	$992.97	$993.00	$992.90