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	$166.94	3.266%	$172.3923	$172.39	$172.40	$172.40
Purchase #2	$72.41	13.334%	$82.0651	$82.07	$82.05	$82.10
Purchase #3	$137.82	12.633%	$155.2308	$155.23	$155.25	$155.20
Purchase #4	$33.83	8.403%	$36.6727	$36.67	$36.65	$36.70
Purchase #5	$47.44	5.711%	$50.1493	$50.15	$50.15	$50.10
Purchase #6	$42.57	6.127%	$45.1783	$45.18	$45.20	$45.20
Purchase #7	$208.47	9.464%	$228.1996	$228.20	$228.20	$228.20
7 purchase totals =	$709.48		$769.8881	$769.89	$769.90	$769.90