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	$40.88	10.485%	$45.1663	$45.17	$45.15	$45.20
Purchase #2	$117.63	11.800%	$131.5103	$131.51	$131.50	$131.50
Purchase #3	$167.64	8.343%	$181.6262	$181.63	$181.65	$181.60
Purchase #4	$81.74	13.711%	$92.9474	$92.95	$92.95	$92.90
Purchase #5	$28.87	6.295%	$30.6874	$30.69	$30.70	$30.70
Purchase #6	$89.85	10.681%	$99.4469	$99.45	$99.45	$99.40
Purchase #7	$23.69	5.124%	$24.9039	$24.90	$24.90	$24.90
7 purchase totals =	$550.30		$606.2884	$606.30	$606.30	$606.20