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	$110.51	11.477%	$123.1932	$123.19	$123.20	$123.20
Purchase #2	$83.37	4.336%	$86.9849	$86.98	$87.00	$87.00
Purchase #3	$101.59	11.119%	$112.8858	$112.89	$112.90	$112.90
Purchase #4	$243.74	12.830%	$275.0118	$275.01	$275.00	$275.00
Purchase #5	$96.71	4.266%	$100.8356	$100.84	$100.85	$100.80
Purchase #6	$211.56	13.672%	$240.4845	$240.48	$240.50	$240.50
Purchase #7	$36.78	3.260%	$37.979	$37.98	$38.00	$38.00
7 purchase totals =	$884.26		$977.3748	$977.37	$977.45	$977.40