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	$139.69	3.841%	$145.0555	$145.06	$145.05	$145.10
Purchase #2	$69.56	4.288%	$72.5427	$72.54	$72.55	$72.50
Purchase #3	$246.29	11.821%	$275.4039	$275.40	$275.40	$275.40
Purchase #4	$234.32	12.523%	$263.6639	$263.66	$263.65	$263.70
Purchase #5	$51.47	12.860%	$58.089	$58.09	$58.10	$58.10
Purchase #6	$41.91	4.514%	$43.8018	$43.80	$43.80	$43.80
Purchase #7	$17.32	11.658%	$19.3392	$19.34	$19.35	$19.30
7 purchase totals =	$800.56		$877.8960	$877.89	$877.90	$877.90