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	$73.93	12.124%	$82.8933	$82.89	$82.90	$82.90
Purchase #2	$144.97	3.516%	$150.0671	$150.07	$150.05	$150.10
Purchase #3	$129.39	7.680%	$139.3272	$139.33	$139.35	$139.30
Purchase #4	$81.91	9.390%	$89.6013	$89.60	$89.60	$89.60
Purchase #5	$173.86	3.542%	$180.0181	$180.02	$180.00	$180.00
Purchase #6	$81.89	13.333%	$92.8084	$92.81	$92.80	$92.80
Purchase #7	$175.36	4.720%	$183.637	$183.64	$183.65	$183.60
7 purchase totals =	$861.31		$918.3524	$918.36	$918.35	$918.30