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	$173.43	6.780%	$185.1886	$185.19	$185.20	$185.20
Purchase #2	$194.60	4.492%	$203.3414	$203.34	$203.35	$203.30
Purchase #3	$55.49	12.253%	$62.2892	$62.29	$62.30	$62.30
Purchase #4	$40.67	11.780%	$45.4609	$45.46	$45.45	$45.50
Purchase #5	$201.46	11.660%	$224.9502	$224.95	$224.95	$225.00
Purchase #6	$62.98	3.113%	$64.9406	$64.94	$64.95	$64.90
Purchase #7	$67.63	4.312%	$70.5462	$70.55	$70.55	$70.50
7 purchase totals =	$796.26		$856.7171	$856.72	$856.75	$856.70