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	$242.78	4.351%	$253.3434	$253.34	$253.35	$253.30
Purchase #2	$25.96	9.746%	$28.4901	$28.49	$28.50	$28.50
Purchase #3	$206.65	12.234%	$231.9316	$231.93	$231.95	$231.90
Purchase #4	$60.59	10.445%	$66.9186	$66.92	$66.90	$66.90
Purchase #5	$239.39	10.288%	$264.0184	$264.02	$264.00	$264.00
Purchase #6	$188.67	6.128%	$200.2317	$200.23	$200.25	$200.20
Purchase #7	$39.65	7.710%	$42.707	$42.71	$42.70	$42.70
7 purchase totals =	$1,003.69		$1,087.6408	$1,087.64	$1,087.65	$1,087.50