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	$152.28	5.511%	$160.6722	$160.67	$160.65	$160.70
Purchase #2	$199.52	11.187%	$221.8403	$221.84	$221.85	$221.80
Purchase #3	$123.78	13.273%	$140.2093	$140.21	$140.20	$140.20
Purchase #4	$171.52	8.327%	$185.8025	$185.80	$185.80	$185.80
Purchase #5	$99.44	10.499%	$109.8802	$109.88	$109.90	$109.90
Purchase #6	$134.91	6.389%	$143.5294	$143.53	$143.55	$143.50
Purchase #7	$35.90	3.274%	$37.0754	$37.08	$37.10	$37.10
7 purchase totals =	$917.35		$999.0093	$999.01	$999.05	$999.00