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	$250.75	4.398%	$261.778	$261.78	$261.80	$261.80
Purchase #2	$164.49	12.265%	$184.6647	$184.66	$184.65	$184.70
Purchase #3	$177.67	3.809%	$184.4375	$184.44	$184.45	$184.40
Purchase #4	$246.82	11.725%	$275.7596	$275.76	$275.75	$275.80
Purchase #5	$153.50	7.600%	$165.166	$165.17	$165.15	$165.20
Purchase #6	$32.43	10.386%	$35.7982	$35.80	$35.80	$35.80
Purchase #7	$86.69	4.770%	$90.8251	$90.83	$90.85	$90.80
7 purchase totals =	$1,112.35		$1,198.4291	$1,198.44	$1,198.45	$1,198.50