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	$127.41	10.176%	$140.3752	$140.38	$140.40	$140.40
Purchase #2	$161.59	11.609%	$180.349	$180.35	$180.35	$180.30
Purchase #3	$127.76	11.421%	$142.3515	$142.35	$142.35	$142.40
Purchase #4	$249.45	3.410%	$257.9562	$257.96	$257.95	$258.00
Purchase #5	$161.30	13.778%	$183.5239	$183.52	$183.50	$183.50
Purchase #6	$232.69	5.846%	$246.2931	$246.29	$246.30	$246.30
Purchase #7	$63.46	12.229%	$71.2205	$71.22	$71.20	$71.20
7 purchase totals =	$1,123.66		$1,222.0694	$1,222.07	$1,222.05	$1,222.10