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	$186.40	6.340%	$198.2178	$198.22	$198.20	$198.20
Purchase #2	$36.34	5.847%	$38.4648	$38.46	$38.45	$38.50
Purchase #3	$238.99	12.659%	$269.2437	$269.24	$269.25	$269.20
Purchase #4	$35.51	9.506%	$38.8856	$38.89	$38.90	$38.90
Purchase #5	$205.52	3.554%	$212.8242	$212.82	$212.80	$212.80
Purchase #6	$201.31	7.736%	$216.8833	$216.88	$216.90	$216.90
Purchase #7	$209.40	13.667%	$238.0187	$238.02	$238.00	$238.00
7 purchase totals =	$1,113.47		$1,212.5381	$1,212.53	$1,212.50	$1,212.50