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	$86.78	3.774%	$90.0551	$90.06	$90.05	$90.10
Purchase #2	$111.97	9.798%	$122.9408	$122.94	$122.95	$122.90
Purchase #3	$113.50	10.402%	$125.3063	$125.31	$125.30	$125.30
Purchase #4	$57.91	10.673%	$64.0907	$64.09	$64.10	$64.10
Purchase #5	$199.86	3.346%	$206.5473	$206.55	$206.55	$206.50
Purchase #6	$247.90	10.282%	$273.3891	$273.39	$273.40	$273.40
Purchase #7	$196.85	13.188%	$222.8106	$222.81	$222.80	$222.80
7 purchase totals =	$1,014.77		$1,105.1399	$1,105.15	$1,105.15	$1,105.10