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	$29.98	4.507%	$31.3312	$31.33	$31.35	$31.30
Purchase #2	$162.38	12.146%	$182.1027	$182.10	$182.10	$182.10
Purchase #3	$78.41	12.574%	$88.2693	$88.27	$88.25	$88.30
Purchase #4	$155.74	13.530%	$176.8116	$176.81	$176.80	$176.80
Purchase #5	$86.70	9.375%	$94.8281	$94.83	$94.85	$94.80
Purchase #6	$40.51	5.850%	$42.8798	$42.88	$42.90	$42.90
Purchase #7	$104.31	10.508%	$115.2709	$115.27	$115.25	$115.30
7 purchase totals =	$658.03		$731.4936	$731.49	$731.50	$731.50