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	$73.64	6.289%	$78.2712	$78.27	$78.25	$78.30
Purchase #2	$65.54	11.499%	$73.0764	$73.08	$73.10	$73.10
Purchase #3	$71.33	3.497%	$73.8244	$73.82	$73.80	$73.80
Purchase #4	$220.54	9.560%	$241.6236	$241.62	$241.60	$241.60
Purchase #5	$132.25	11.776%	$147.8238	$147.82	$147.80	$147.80
Purchase #6	$44.29	10.417%	$48.9037	$48.90	$48.90	$48.90
Purchase #7	$182.89	12.213%	$205.2264	$205.23	$205.25	$205.20
7 purchase totals =	$790.48		$868.7495	$868.74	$868.70	$868.70