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	$186.33	12.124%	$208.9206	$208.92	$208.90	$208.90
Purchase #2	$52.99	12.222%	$59.4664	$59.47	$59.45	$59.50
Purchase #3	$182.36	9.206%	$199.1481	$199.15	$199.15	$199.10
Purchase #4	$20.50	6.866%	$21.9075	$21.91	$21.90	$21.90
Purchase #5	$225.36	6.688%	$240.4321	$240.43	$240.45	$240.40
Purchase #6	$223.32	6.177%	$237.1145	$237.11	$237.10	$237.10
Purchase #7	$6.32	4.679%	$6.6157	$6.62	$6.60	$6.60
7 purchase totals =	$897.18		$973.6049	$973.61	$973.55	$973.50