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	$48.64	8.542%	$52.7948	$52.79	$52.80	$52.80
Purchase #2	$70.62	11.376%	$78.6537	$78.65	$78.65	$78.70
Purchase #3	$152.46	8.145%	$164.8779	$164.88	$164.90	$164.90
Purchase #4	$85.34	5.462%	$90.0013	$90.00	$90.00	$90.00
Purchase #5	$54.79	3.119%	$56.4989	$56.50	$56.50	$56.50
Purchase #6	$237.60	3.473%	$245.8518	$245.85	$245.85	$245.90
Purchase #7	$93.76	7.874%	$101.1427	$101.14	$101.15	$101.10
7 purchase totals =	$743.21		$789.8211	$789.81	$789.85	$789.90