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	$72.25	13.698%	$82.1468	$82.15	$82.15	$82.10
Purchase #2	$83.34	9.543%	$91.2931	$91.29	$91.30	$91.30
Purchase #3	$20.85	13.772%	$23.7215	$23.72	$23.70	$23.70
Purchase #4	$174.50	3.860%	$181.2357	$181.24	$181.25	$181.20
Purchase #5	$133.30	5.557%	$140.7075	$140.71	$140.70	$140.70
Purchase #6	$207.62	5.738%	$219.5332	$219.53	$219.55	$219.50
Purchase #7	$19.48	4.178%	$20.2939	$20.29	$20.30	$20.30
7 purchase totals =	$711.34		$758.9317	$758.93	$758.95	$758.80