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	$21.38	13.215%	$24.2054	$24.21	$24.20	$24.20
Purchase #2	$38.89	8.331%	$42.1299	$42.13	$42.15	$42.10
Purchase #3	$204.96	6.161%	$217.5876	$217.59	$217.60	$217.60
Purchase #4	$123.97	7.473%	$133.2343	$133.23	$133.25	$133.20
Purchase #5	$39.77	10.377%	$43.8969	$43.90	$43.90	$43.90
Purchase #6	$209.85	5.449%	$221.2847	$221.28	$221.30	$221.30
Purchase #7	$55.58	6.465%	$59.1732	$59.17	$59.15	$59.20
7 purchase totals =	$694.40		$741.5120	$741.51	$741.55	$741.50