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	$122.54	11.281%	$136.3637	$136.36	$136.35	$136.40
Purchase #2	$230.61	3.183%	$237.9503	$237.95	$237.95	$238.00
Purchase #3	$235.60	11.155%	$261.8812	$261.88	$261.90	$261.90
Purchase #4	$10.28	12.222%	$11.5364	$11.54	$11.55	$11.50
Purchase #5	$110.71	11.391%	$123.321	$123.32	$123.30	$123.30
Purchase #6	$139.32	4.712%	$145.8848	$145.88	$145.90	$145.90
Purchase #7	$247.81	10.256%	$273.2254	$273.23	$273.25	$273.20
7 purchase totals =	$1,096.87		$1,190.1628	$1,190.16	$1,190.20	$1,190.20