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	$141.33	12.164%	$158.5214	$158.52	$158.50	$158.50
Purchase #2	$218.34	10.269%	$240.7613	$240.76	$240.75	$240.80
Purchase #3	$158.34	4.199%	$164.9887	$164.99	$165.00	$165.00
Purchase #4	$84.78	7.312%	$90.9791	$90.98	$91.00	$91.00
Purchase #5	$38.81	13.214%	$43.9384	$43.94	$43.95	$43.90
Purchase #6	$78.76	9.613%	$86.3312	$86.33	$86.35	$86.30
Purchase #7	$210.85	6.551%	$224.6628	$224.66	$224.65	$224.70
7 purchase totals =	$931.21		$1,010.1829	$1,010.18	$1,010.20	$1,010.20