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	$33.66	13.308%	$38.1395	$38.14	$38.15	$38.10
Purchase #2	$42.55	6.785%	$45.437	$45.44	$45.45	$45.40
Purchase #3	$220.57	11.272%	$245.4327	$245.43	$245.45	$245.40
Purchase #4	$176.97	12.108%	$198.3975	$198.40	$198.40	$198.40
Purchase #5	$84.89	6.794%	$90.6574	$90.66	$90.65	$90.70
Purchase #6	$169.59	5.505%	$178.9259	$178.93	$178.95	$178.90
Purchase #7	$199.57	5.492%	$210.5304	$210.53	$210.55	$210.50
7 purchase totals =	$927.80		$1,007.5204	$1,007.53	$1,007.60	$1,007.40