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	$243.43	8.453%	$264.0071	$264.01	$264.00	$264.00
Purchase #2	$35.70	7.363%	$38.3286	$38.33	$38.35	$38.30
Purchase #3	$182.83	4.231%	$190.5655	$190.57	$190.55	$190.60
Purchase #4	$29.34	13.238%	$33.224	$33.22	$33.20	$33.20
Purchase #5	$199.97	8.292%	$216.5515	$216.55	$216.55	$216.60
Purchase #6	$199.49	8.518%	$216.4826	$216.48	$216.50	$216.50
Purchase #7	$78.78	6.205%	$83.6683	$83.67	$83.65	$83.70
7 purchase totals =	$969.54		$1,042.8276	$1,042.83	$1,042.80	$1,042.90