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	$6.99	10.817%	$7.7461	$7.75	$7.75	$7.70
Purchase #2	$82.37	6.742%	$87.9234	$87.92	$87.90	$87.90
Purchase #3	$126.95	11.762%	$141.8819	$141.88	$141.90	$141.90
Purchase #4	$73.69	6.779%	$78.6854	$78.69	$78.70	$78.70
Purchase #5	$197.43	13.392%	$223.8698	$223.87	$223.85	$223.90
Purchase #6	$91.86	4.127%	$95.6511	$95.65	$95.65	$95.70
Purchase #7	$155.48	5.703%	$164.347	$164.35	$164.35	$164.30
7 purchase totals =	$734.77		$800.1047	$800.11	$800.10	$800.10