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	$111.29	8.672%	$120.9411	$120.94	$120.95	$120.90
Purchase #2	$213.73	3.595%	$221.4136	$221.41	$221.40	$221.40
Purchase #3	$86.31	10.621%	$95.477	$95.48	$95.50	$95.50
Purchase #4	$30.48	6.843%	$32.5657	$32.57	$32.55	$32.60
Purchase #5	$156.51	5.316%	$164.8301	$164.83	$164.85	$164.80
Purchase #6	$51.69	10.706%	$57.2239	$57.22	$57.20	$57.20
Purchase #7	$151.50	13.225%	$171.5359	$171.54	$171.55	$171.50
7 purchase totals =	$801.51		$863.9873	$863.99	$864.00	$863.90