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	$33.79	11.500%	$37.6759	$37.68	$37.70	$37.70
Purchase #2	$61.42	3.815%	$63.7632	$63.76	$63.75	$63.80
Purchase #3	$53.55	10.265%	$59.0469	$59.05	$59.05	$59.00
Purchase #4	$170.90	8.704%	$185.7751	$185.78	$185.80	$185.80
Purchase #5	$112.77	10.127%	$124.1902	$124.19	$124.20	$124.20
Purchase #6	$196.38	12.581%	$221.0866	$221.09	$221.10	$221.10
Purchase #7	$20.89	7.841%	$22.528	$22.53	$22.55	$22.50
7 purchase totals =	$649.70		$714.0659	$714.08	$714.15	$714.10