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	$43.58	10.599%	$48.199	$48.20	$48.20	$48.20
Purchase #2	$140.96	8.497%	$152.9374	$152.94	$152.95	$152.90
Purchase #3	$83.84	6.205%	$89.0423	$89.04	$89.05	$89.00
Purchase #4	$250.42	9.520%	$274.26	$274.26	$274.25	$274.30
Purchase #5	$81.34	10.473%	$89.8587	$89.86	$89.85	$89.90
Purchase #6	$69.88	4.561%	$73.0672	$73.07	$73.05	$73.10
Purchase #7	$91.83	12.114%	$102.9543	$102.95	$102.95	$103.00
7 purchase totals =	$761.85		$830.3189	$830.32	$830.30	$830.40