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	$42.51	11.189%	$47.2664	$47.27	$47.25	$47.30
Purchase #2	$149.90	13.345%	$169.9042	$169.90	$169.90	$169.90
Purchase #3	$178.67	6.529%	$190.3354	$190.34	$190.35	$190.30
Purchase #4	$110.46	8.263%	$119.5873	$119.59	$119.60	$119.60
Purchase #5	$14.57	9.254%	$15.9183	$15.92	$15.90	$15.90
Purchase #6	$141.84	4.405%	$148.0881	$148.09	$148.10	$148.10
Purchase #7	$198.57	12.364%	$223.1212	$223.12	$223.10	$223.10
7 purchase totals =	$836.52		$914.2209	$914.23	$914.20	$914.20