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	$114.74	4.127%	$119.4753	$119.48	$119.50	$119.50
Purchase #2	$18.48	11.153%	$20.5411	$20.54	$20.55	$20.50
Purchase #3	$235.64	6.335%	$250.5678	$250.57	$250.55	$250.60
Purchase #4	$114.29	10.759%	$126.5865	$126.59	$126.60	$126.60
Purchase #5	$90.44	3.614%	$93.7085	$93.71	$93.70	$93.70
Purchase #6	$159.78	6.109%	$169.541	$169.54	$169.55	$169.50
Purchase #7	$68.30	6.807%	$72.9492	$72.95	$72.95	$72.90
7 purchase totals =	$801.67		$853.3694	$853.38	$853.40	$853.30