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	$125.35	13.650%	$142.4603	$142.46	$142.45	$142.50
Purchase #2	$137.34	3.302%	$141.875	$141.88	$141.90	$141.90
Purchase #3	$152.26	5.513%	$160.6541	$160.65	$160.65	$160.70
Purchase #4	$96.83	4.313%	$101.0063	$101.01	$101.00	$101.00
Purchase #5	$37.45	12.188%	$42.0144	$42.01	$42.00	$42.00
Purchase #6	$19.43	5.859%	$20.5684	$20.57	$20.55	$20.60
Purchase #7	$130.84	11.786%	$146.2608	$146.26	$146.25	$146.30
7 purchase totals =	$699.50		$754.8393	$754.84	$754.80	$755.00