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	$9.31	12.689%	$10.4913	$10.49	$10.50	$10.50
Purchase #2	$209.86	5.339%	$221.0644	$221.06	$221.05	$221.10
Purchase #3	$33.62	10.217%	$37.055	$37.06	$37.05	$37.10
Purchase #4	$131.83	12.133%	$147.8249	$147.82	$147.80	$147.80
Purchase #5	$78.97	12.497%	$88.8389	$88.84	$88.85	$88.80
Purchase #6	$84.38	7.471%	$90.684	$90.68	$90.70	$90.70
Purchase #7	$69.69	3.227%	$71.9389	$71.94	$71.95	$71.90
7 purchase totals =	$617.66		$667.8974	$667.89	$667.90	$667.90