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	$150.54	12.225%	$168.9435	$168.94	$168.95	$168.90
Purchase #2	$164.25	9.168%	$179.3084	$179.31	$179.30	$179.30
Purchase #3	$21.27	13.655%	$24.1744	$24.17	$24.15	$24.20
Purchase #4	$31.84	3.334%	$32.9015	$32.90	$32.90	$32.90
Purchase #5	$83.84	7.304%	$89.9637	$89.96	$89.95	$90.00
Purchase #6	$187.84	6.225%	$199.533	$199.53	$199.55	$199.50
Purchase #7	$82.45	9.507%	$90.2885	$90.29	$90.30	$90.30
7 purchase totals =	$722.03		$785.1130	$785.10	$785.10	$785.10