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	$72.36	13.735%	$82.2986	$82.30	$82.30	$82.30
Purchase #2	$57.34	7.115%	$61.4197	$61.42	$61.40	$61.40
Purchase #3	$123.27	10.714%	$136.4771	$136.48	$136.50	$136.50
Purchase #4	$101.33	11.569%	$113.0529	$113.05	$113.05	$113.10
Purchase #5	$40.86	6.393%	$43.4722	$43.47	$43.45	$43.50
Purchase #6	$123.50	6.312%	$131.2953	$131.30	$131.30	$131.30
Purchase #7	$95.49	3.204%	$98.5495	$98.55	$98.55	$98.50
7 purchase totals =	$614.15		$666.5653	$666.57	$666.55	$666.60