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	$121.91	8.175%	$131.8761	$131.88	$131.90	$131.90
Purchase #2	$132.95	11.721%	$148.5331	$148.53	$148.55	$148.50
Purchase #3	$43.64	8.291%	$47.2582	$47.26	$47.25	$47.30
Purchase #4	$7.29	11.267%	$8.1114	$8.11	$8.10	$8.10
Purchase #5	$38.59	8.703%	$41.9485	$41.95	$41.95	$41.90
Purchase #6	$75.99	3.773%	$78.8571	$78.86	$78.85	$78.90
Purchase #7	$85.40	4.523%	$89.2626	$89.26	$89.25	$89.30
7 purchase totals =	$505.77		$545.8470	$545.85	$545.85	$545.90