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	$136.89	4.867%	$143.5524	$143.55	$143.55	$143.60
Purchase #2	$36.85	13.678%	$41.8903	$41.89	$41.90	$41.90
Purchase #3	$204.66	3.598%	$212.0237	$212.02	$212.00	$212.00
Purchase #4	$6.78	5.637%	$7.1622	$7.16	$7.15	$7.20
Purchase #5	$133.48	12.837%	$150.6148	$150.61	$150.60	$150.60
Purchase #6	$232.61	5.387%	$245.1407	$245.14	$245.15	$245.10
Purchase #7	$42.70	6.759%	$45.5861	$45.59	$45.60	$45.60
7 purchase totals =	$793.97		$845.9702	$845.96	$845.95	$846.00