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	$89.46	3.381%	$92.4846	$92.48	$92.50	$92.50
Purchase #2	$79.79	13.336%	$90.4308	$90.43	$90.45	$90.40
Purchase #3	$108.92	3.115%	$112.3129	$112.31	$112.30	$112.30
Purchase #4	$121.84	7.819%	$131.3667	$131.37	$131.35	$131.40
Purchase #5	$131.46	12.568%	$147.9819	$147.98	$148.00	$148.00
Purchase #6	$183.47	9.451%	$200.8097	$200.81	$200.80	$200.80
Purchase #7	$80.28	13.446%	$91.0744	$91.07	$91.05	$91.10
7 purchase totals =	$795.22		$866.4610	$866.45	$866.45	$866.50