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	$179.38	10.816%	$198.7817	$198.78	$198.80	$198.80
Purchase #2	$215.63	6.611%	$229.8853	$229.89	$229.90	$229.90
Purchase #3	$112.25	3.595%	$116.2854	$116.29	$116.30	$116.30
Purchase #4	$50.93	12.435%	$57.2631	$57.26	$57.25	$57.30
Purchase #5	$97.83	13.573%	$111.1085	$111.11	$111.10	$111.10
Purchase #6	$33.79	7.549%	$36.3408	$36.34	$36.35	$36.30
Purchase #7	$35.94	12.486%	$40.4275	$40.43	$40.45	$40.40
7 purchase totals =	$725.75		$790.0923	$790.10	$790.15	$790.10