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	$240.52	13.557%	$273.1273	$273.13	$273.15	$273.10
Purchase #2	$72.94	7.390%	$78.3303	$78.33	$78.35	$78.30
Purchase #3	$38.44	12.766%	$43.3473	$43.35	$43.35	$43.30
Purchase #4	$22.81	12.519%	$25.6656	$25.67	$25.65	$25.70
Purchase #5	$212.56	4.344%	$221.7936	$221.79	$221.80	$221.80
Purchase #6	$67.83	7.565%	$72.9613	$72.96	$72.95	$73.00
Purchase #7	$21.80	13.126%	$24.6615	$24.66	$24.65	$24.70
7 purchase totals =	$676.90		$739.8869	$739.89	$739.90	$739.90