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	$129.49	10.298%	$142.8249	$142.82	$142.80	$142.80
Purchase #2	$167.68	3.270%	$173.1631	$173.16	$173.15	$173.20
Purchase #3	$125.37	12.515%	$141.0601	$141.06	$141.05	$141.10
Purchase #4	$57.90	8.553%	$62.8522	$62.85	$62.85	$62.90
Purchase #5	$86.65	11.624%	$96.7222	$96.72	$96.70	$96.70
Purchase #6	$124.76	9.209%	$136.2491	$136.25	$136.25	$136.20
Purchase #7	$76.56	3.124%	$78.9517	$78.95	$78.95	$79.00
7 purchase totals =	$768.41		$831.8233	$831.81	$831.75	$831.90