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	$235.81	7.688%	$253.9391	$253.94	$253.95	$253.90
Purchase #2	$82.41	9.808%	$90.4928	$90.49	$90.50	$90.50
Purchase #3	$77.36	11.488%	$86.2471	$86.25	$86.25	$86.20
Purchase #4	$51.47	6.680%	$54.9082	$54.91	$54.90	$54.90
Purchase #5	$5.51	8.565%	$5.9819	$5.98	$6.00	$6.00
Purchase #6	$92.78	12.349%	$104.2374	$104.24	$104.25	$104.20
Purchase #7	$234.61	8.839%	$255.3472	$255.35	$255.35	$255.30
7 purchase totals =	$779.95		$851.1537	$851.16	$851.20	$851.00