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	$245.60	11.217%	$273.149	$273.15	$273.15	$273.10
Purchase #2	$220.50	11.730%	$246.3647	$246.36	$246.35	$246.40
Purchase #3	$156.33	5.468%	$164.8781	$164.88	$164.90	$164.90
Purchase #4	$95.60	7.795%	$103.052	$103.05	$103.05	$103.10
Purchase #5	$66.34	7.365%	$71.2259	$71.23	$71.25	$71.20
Purchase #6	$158.31	9.200%	$172.8745	$172.87	$172.85	$172.90
Purchase #7	$86.91	12.279%	$97.5817	$97.58	$97.60	$97.60
7 purchase totals =	$1,029.59		$1,129.1259	$1,129.12	$1,129.15	$1,129.20