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	$152.36	12.818%	$171.8895	$171.89	$171.90	$171.90
Purchase #2	$132.72	7.635%	$142.8532	$142.85	$142.85	$142.90
Purchase #3	$73.82	3.765%	$76.5993	$76.60	$76.60	$76.60
Purchase #4	$18.91	12.586%	$21.29	$21.29	$21.30	$21.30
Purchase #5	$206.86	6.387%	$220.0721	$220.07	$220.05	$220.10
Purchase #6	$109.79	4.285%	$114.4945	$114.49	$114.50	$114.50
Purchase #7	$139.72	9.664%	$153.2225	$153.22	$153.20	$153.20
7 purchase totals =	$834.18		$900.4211	$900.41	$900.40	$900.50