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	$38.66	9.638%	$42.3861	$42.39	$42.40	$42.40
Purchase #2	$164.44	6.329%	$174.8474	$174.85	$174.85	$174.80
Purchase #3	$109.36	12.804%	$123.3625	$123.36	$123.35	$123.40
Purchase #4	$235.38	12.166%	$264.0163	$264.02	$264.00	$264.00
Purchase #5	$81.48	4.568%	$85.202	$85.20	$85.20	$85.20
Purchase #6	$176.38	10.156%	$194.2932	$194.29	$194.30	$194.30
Purchase #7	$37.95	10.686%	$42.0053	$42.01	$42.00	$42.00
7 purchase totals =	$843.65		$926.1128	$926.12	$926.10	$926.10