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	$43.86	11.336%	$48.832	$48.83	$48.85	$48.80
Purchase #2	$34.27	4.415%	$35.783	$35.78	$35.80	$35.80
Purchase #3	$81.71	9.383%	$89.3768	$89.38	$89.40	$89.40
Purchase #4	$123.75	12.355%	$139.0393	$139.04	$139.05	$139.00
Purchase #5	$248.33	12.524%	$279.4308	$279.43	$279.45	$279.40
Purchase #6	$64.25	9.592%	$70.4129	$70.41	$70.40	$70.40
Purchase #7	$115.57	8.576%	$125.4813	$125.48	$125.50	$125.50
7 purchase totals =	$711.74		$788.3561	$788.35	$788.45	$788.30