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	$112.34	11.558%	$125.3243	$125.32	$125.30	$125.30
Purchase #2	$69.76	4.483%	$72.8873	$72.89	$72.90	$72.90
Purchase #3	$11.46	4.819%	$12.0123	$12.01	$12.00	$12.00
Purchase #4	$72.42	5.540%	$76.4321	$76.43	$76.45	$76.40
Purchase #5	$69.80	5.260%	$73.4715	$73.47	$73.45	$73.50
Purchase #6	$125.70	11.609%	$140.2925	$140.29	$140.30	$140.30
Purchase #7	$78.38	7.830%	$84.5172	$84.52	$84.50	$84.50
7 purchase totals =	$539.86		$584.9372	$584.93	$584.90	$584.90