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	$55.62	7.682%	$59.8927	$59.89	$59.90	$59.90
Purchase #2	$29.68	3.550%	$30.7336	$30.73	$30.75	$30.70
Purchase #3	$162.37	3.432%	$167.9425	$167.94	$167.95	$167.90
Purchase #4	$70.78	10.830%	$78.4455	$78.45	$78.45	$78.40
Purchase #5	$225.41	3.387%	$233.0446	$233.04	$233.05	$233.00
Purchase #6	$32.30	9.705%	$35.4347	$35.43	$35.45	$35.40
Purchase #7	$200.86	5.778%	$212.4657	$212.47	$212.45	$212.50
7 purchase totals =	$777.02		$817.9593	$817.95	$818.00	$817.80