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	$71.93	13.687%	$81.7751	$81.78	$81.80	$81.80
Purchase #2	$114.78	10.242%	$126.5358	$126.54	$126.55	$126.50
Purchase #3	$223.97	11.148%	$248.9382	$248.94	$248.95	$248.90
Purchase #4	$82.68	7.696%	$89.0431	$89.04	$89.05	$89.00
Purchase #5	$99.99	10.436%	$110.425	$110.43	$110.45	$110.40
Purchase #6	$38.50	8.763%	$41.8738	$41.87	$41.85	$41.90
Purchase #7	$179.33	9.575%	$196.5008	$196.50	$196.50	$196.50
7 purchase totals =	$811.18		$895.0918	$895.10	$895.15	$895.00