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	$128.35	8.667%	$139.4741	$139.47	$139.45	$139.50
Purchase #2	$123.35	5.654%	$130.3242	$130.32	$130.30	$130.30
Purchase #3	$229.30	11.655%	$256.0249	$256.02	$256.00	$256.00
Purchase #4	$245.53	6.109%	$260.5294	$260.53	$260.55	$260.50
Purchase #5	$29.34	13.429%	$33.2801	$33.28	$33.30	$33.30
Purchase #6	$56.29	8.433%	$61.0369	$61.04	$61.05	$61.00
Purchase #7	$23.88	7.843%	$25.7529	$25.75	$25.75	$25.80
7 purchase totals =	$836.04		$906.4225	$906.41	$906.40	$906.40