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	$16.30	6.205%	$17.3114	$17.31	$17.30	$17.30
Purchase #2	$211.37	13.774%	$240.4841	$240.48	$240.50	$240.50
Purchase #3	$37.65	12.750%	$42.4504	$42.45	$42.45	$42.50
Purchase #4	$209.34	6.131%	$222.1746	$222.17	$222.15	$222.20
Purchase #5	$77.86	5.329%	$82.0092	$82.01	$82.00	$82.00
Purchase #6	$48.40	3.223%	$49.9599	$49.96	$49.95	$50.00
Purchase #7	$193.87	3.458%	$200.574	$200.57	$200.55	$200.60
7 purchase totals =	$794.79		$854.9636	$854.95	$854.90	$855.10