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	$135.79	6.700%	$144.8879	$144.89	$144.90	$144.90
Purchase #2	$127.29	3.334%	$131.5338	$131.53	$131.55	$131.50
Purchase #3	$43.64	8.836%	$47.496	$47.50	$47.50	$47.50
Purchase #4	$7.90	11.480%	$8.8069	$8.81	$8.80	$8.80
Purchase #5	$59.73	3.705%	$61.943	$61.94	$61.95	$61.90
Purchase #6	$214.28	8.865%	$233.2759	$233.28	$233.30	$233.30
Purchase #7	$210.94	4.766%	$220.9934	$220.99	$221.00	$221.00
7 purchase totals =	$799.57		$848.9369	$848.94	$849.00	$848.90