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	$128.40	12.355%	$144.2638	$144.26	$144.25	$144.30
Purchase #2	$113.28	10.255%	$124.8969	$124.90	$124.90	$124.90
Purchase #3	$137.90	9.185%	$150.5661	$150.57	$150.55	$150.60
Purchase #4	$173.78	6.575%	$185.206	$185.21	$185.20	$185.20
Purchase #5	$38.31	10.504%	$42.3341	$42.33	$42.35	$42.30
Purchase #6	$168.83	4.771%	$176.8849	$176.88	$176.90	$176.90
Purchase #7	$247.45	8.659%	$268.8767	$268.88	$268.90	$268.90
7 purchase totals =	$1,007.95		$1,093.0285	$1,093.03	$1,093.05	$1,093.10