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	$59.87	12.807%	$67.5376	$67.54	$67.55	$67.50
Purchase #2	$53.38	9.419%	$58.4079	$58.41	$58.40	$58.40
Purchase #3	$102.78	9.337%	$112.3766	$112.38	$112.40	$112.40
Purchase #4	$222.98	8.599%	$242.1541	$242.15	$242.15	$242.20
Purchase #5	$168.53	12.116%	$188.9491	$188.95	$188.95	$188.90
Purchase #6	$119.35	6.623%	$127.2546	$127.25	$127.25	$127.30
Purchase #7	$199.93	5.444%	$210.8142	$210.81	$210.80	$210.80
7 purchase totals =	$926.82		$1,007.4941	$1,007.49	$1,007.50	$1,007.50