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	$31.63	13.627%	$35.9402	$35.94	$35.95	$35.90
Purchase #2	$57.64	3.235%	$59.5047	$59.50	$59.50	$59.50
Purchase #3	$94.76	5.392%	$99.8695	$99.87	$99.85	$99.90
Purchase #4	$39.51	5.183%	$41.5578	$41.56	$41.55	$41.60
Purchase #5	$194.78	13.353%	$220.789	$220.79	$220.80	$220.80
Purchase #6	$169.69	7.806%	$182.936	$182.94	$182.95	$182.90
Purchase #7	$72.37	9.317%	$79.1127	$79.11	$79.10	$79.10
7 purchase totals =	$660.38		$719.7099	$719.71	$719.70	$719.70