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	$44.89	5.793%	$47.4905	$47.49	$47.50	$47.50
Purchase #2	$83.86	12.767%	$94.5664	$94.57	$94.55	$94.60
Purchase #3	$72.78	6.293%	$77.36	$77.36	$77.35	$77.40
Purchase #4	$100.94	4.149%	$105.128	$105.13	$105.15	$105.10
Purchase #5	$50.68	3.349%	$52.3773	$52.38	$52.40	$52.40
Purchase #6	$136.41	3.736%	$141.5063	$141.51	$141.50	$141.50
Purchase #7	$100.44	6.642%	$107.1112	$107.11	$107.10	$107.10
7 purchase totals =	$590.00		$625.5397	$625.55	$625.55	$625.60