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	$249.47	8.459%	$270.5727	$270.57	$270.55	$270.60
Purchase #2	$37.78	12.456%	$42.4859	$42.49	$42.50	$42.50
Purchase #3	$249.64	3.804%	$259.1363	$259.14	$259.15	$259.10
Purchase #4	$119.55	9.704%	$131.1511	$131.15	$131.15	$131.20
Purchase #5	$221.97	3.365%	$229.4393	$229.44	$229.45	$229.40
Purchase #6	$136.84	5.874%	$144.878	$144.88	$144.90	$144.90
Purchase #7	$98.78	3.429%	$102.1672	$102.17	$102.15	$102.20
7 purchase totals =	$1,114.03		$1,179.8305	$1,179.84	$1,179.85	$1,179.90