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	$42.36	5.874%	$44.8482	$44.85	$44.85	$44.80
Purchase #2	$16.69	8.418%	$18.095	$18.10	$18.10	$18.10
Purchase #3	$142.50	13.404%	$161.6007	$161.60	$161.60	$161.60
Purchase #4	$11.61	6.236%	$12.334	$12.33	$12.35	$12.30
Purchase #5	$183.46	6.781%	$195.9004	$195.90	$195.90	$195.90
Purchase #6	$80.57	10.799%	$89.2708	$89.27	$89.25	$89.30
Purchase #7	$134.89	8.407%	$146.2302	$146.23	$146.25	$146.20
7 purchase totals =	$612.08		$668.2793	$668.28	$668.30	$668.20