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	$33.90	11.495%	$37.7968	$37.80	$37.80	$37.80
Purchase #2	$118.65	7.619%	$127.6899	$127.69	$127.70	$127.70
Purchase #3	$136.67	3.469%	$141.4111	$141.41	$141.40	$141.40
Purchase #4	$135.56	9.835%	$148.8923	$148.89	$148.90	$148.90
Purchase #5	$246.74	4.423%	$257.6533	$257.65	$257.65	$257.70
Purchase #6	$9.86	8.164%	$10.665	$10.67	$10.65	$10.70
Purchase #7	$235.92	6.321%	$250.8325	$250.83	$250.85	$250.80
7 purchase totals =	$917.30		$974.9409	$974.94	$974.95	$975.00