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	$98.90	5.669%	$104.5066	$104.51	$104.50	$104.50
Purchase #2	$30.45	3.373%	$31.4771	$31.48	$31.50	$31.50
Purchase #3	$198.35	10.670%	$219.5139	$219.51	$219.50	$219.50
Purchase #4	$78.97	13.288%	$89.4635	$89.46	$89.45	$89.50
Purchase #5	$82.41	13.265%	$93.3417	$93.34	$93.35	$93.30
Purchase #6	$149.90	13.717%	$170.4618	$170.46	$170.45	$170.50
Purchase #7	$100.90	7.701%	$108.6703	$108.67	$108.65	$108.70
7 purchase totals =	$739.88		$817.4349	$817.43	$817.40	$817.50