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	$16.78	4.544%	$17.5425	$17.54	$17.55	$17.50
Purchase #2	$184.76	5.660%	$195.2174	$195.22	$195.20	$195.20
Purchase #3	$213.48	4.240%	$222.5316	$222.53	$222.55	$222.50
Purchase #4	$188.70	6.342%	$200.6674	$200.67	$200.65	$200.70
Purchase #5	$162.39	3.542%	$168.1419	$168.14	$168.15	$168.10
Purchase #6	$93.76	3.789%	$97.3126	$97.31	$97.30	$97.30
Purchase #7	$179.96	10.274%	$198.4491	$198.45	$198.45	$198.40
7 purchase totals =	$1,039.83		$1,099.8625	$1,099.86	$1,099.85	$1,099.70