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	$38.95	4.223%	$40.5949	$40.59	$40.60	$40.60
Purchase #2	$70.84	11.155%	$78.7422	$78.74	$78.75	$78.70
Purchase #3	$123.68	6.569%	$131.8045	$131.80	$131.80	$131.80
Purchase #4	$73.73	3.624%	$76.402	$76.40	$76.40	$76.40
Purchase #5	$21.33	5.398%	$22.4814	$22.48	$22.50	$22.50
Purchase #6	$79.82	3.796%	$82.85	$82.85	$82.85	$82.90
Purchase #7	$152.33	3.220%	$157.235	$157.24	$157.25	$157.20
7 purchase totals =	$560.68		$590.1100	$590.10	$590.15	$590.10