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	$123.67	8.276%	$133.9049	$133.90	$133.90	$133.90
Purchase #2	$88.60	9.293%	$96.8336	$96.83	$96.85	$96.80
Purchase #3	$233.69	9.746%	$256.4654	$256.47	$256.45	$256.50
Purchase #4	$96.92	7.559%	$104.2462	$104.25	$104.25	$104.20
Purchase #5	$229.62	10.714%	$254.2215	$254.22	$254.20	$254.20
Purchase #6	$119.54	9.860%	$131.3266	$131.33	$131.35	$131.30
Purchase #7	$75.33	12.303%	$84.5978	$84.60	$84.60	$84.60
7 purchase totals =	$967.37		$1,061.5960	$1,061.60	$1,061.60	$1,061.50