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	$26.75	6.179%	$28.4029	$28.40	$28.40	$28.40
Purchase #2	$34.91	8.569%	$37.9014	$37.90	$37.90	$37.90
Purchase #3	$51.90	11.202%	$57.7138	$57.71	$57.70	$57.70
Purchase #4	$19.78	10.248%	$21.8071	$21.81	$21.80	$21.80
Purchase #5	$67.50	6.108%	$71.6229	$71.62	$71.60	$71.60
Purchase #6	$137.68	3.285%	$142.2028	$142.20	$142.20	$142.20
Purchase #7	$174.33	12.426%	$195.9922	$195.99	$196.00	$196.00
7 purchase totals =	$512.85		$555.6431	$555.63	$555.60	$555.60