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	$236.81	11.577%	$264.2255	$264.23	$264.25	$264.20
Purchase #2	$193.28	3.500%	$200.0448	$200.04	$200.05	$200.00
Purchase #3	$32.72	9.425%	$35.8039	$35.80	$35.80	$35.80
Purchase #4	$172.65	6.861%	$184.4955	$184.50	$184.50	$184.50
Purchase #5	$59.36	11.811%	$66.371	$66.37	$66.35	$66.40
Purchase #6	$38.71	9.548%	$42.406	$42.41	$42.40	$42.40
Purchase #7	$128.33	12.618%	$144.5227	$144.52	$144.50	$144.50
7 purchase totals =	$861.86		$937.8694	$937.87	$937.85	$937.80