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	$110.98	11.622%	$123.8781	$123.88	$123.90	$123.90
Purchase #2	$131.84	6.544%	$140.4676	$140.47	$140.45	$140.50
Purchase #3	$213.55	4.602%	$223.3776	$223.38	$223.40	$223.40
Purchase #4	$153.97	5.217%	$162.0026	$162.00	$162.00	$162.00
Purchase #5	$139.96	7.563%	$150.5452	$150.55	$150.55	$150.50
Purchase #6	$224.32	8.232%	$242.786	$242.79	$242.80	$242.80
Purchase #7	$55.61	6.427%	$59.1841	$59.18	$59.20	$59.20
7 purchase totals =	$1,030.23		$1,102.2412	$1,102.25	$1,102.30	$1,102.30