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	$39.57	4.545%	$41.3685	$41.37	$41.35	$41.40
Purchase #2	$29.71	3.750%	$30.8241	$30.82	$30.80	$30.80
Purchase #3	$64.59	12.292%	$72.5294	$72.53	$72.55	$72.50
Purchase #4	$209.47	6.711%	$223.5275	$223.53	$223.55	$223.50
Purchase #5	$169.85	6.494%	$180.8801	$180.88	$180.90	$180.90
Purchase #6	$102.60	6.667%	$109.4403	$109.44	$109.45	$109.40
Purchase #7	$185.97	7.839%	$200.5482	$200.55	$200.55	$200.50
7 purchase totals =	$801.76		$859.1181	$859.12	$859.15	$859.00