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	$6.50	5.802%	$6.8771	$6.88	$6.90	$6.90
Purchase #2	$71.89	8.636%	$78.0984	$78.10	$78.10	$78.10
Purchase #3	$115.60	7.106%	$123.8145	$123.81	$123.80	$123.80
Purchase #4	$138.78	8.327%	$150.3362	$150.34	$150.35	$150.30
Purchase #5	$161.45	5.167%	$169.7921	$169.79	$169.80	$169.80
Purchase #6	$109.97	8.328%	$119.1283	$119.13	$119.15	$119.10
Purchase #7	$250.56	9.468%	$274.283	$274.28	$274.30	$274.30
7 purchase totals =	$854.75		$922.3296	$922.33	$922.40	$922.30