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	$102.44	10.564%	$113.2618	$113.26	$113.25	$113.30
Purchase #2	$125.28	12.820%	$141.3409	$141.34	$141.35	$141.30
Purchase #3	$76.31	13.116%	$86.3188	$86.32	$86.30	$86.30
Purchase #4	$155.67	7.154%	$166.8066	$166.81	$166.80	$166.80
Purchase #5	$142.77	7.288%	$153.1751	$153.18	$153.20	$153.20
Purchase #6	$143.79	6.454%	$153.0702	$153.07	$153.05	$153.10
Purchase #7	$98.57	13.589%	$111.9647	$111.96	$111.95	$112.00
7 purchase totals =	$844.83		$925.9381	$925.94	$925.90	$926.00