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	$16.85	9.593%	$18.4664	$18.47	$18.45	$18.50
Purchase #2	$211.59	5.349%	$222.9079	$222.91	$222.90	$222.90
Purchase #3	$77.96	6.794%	$83.2566	$83.26	$83.25	$83.30
Purchase #4	$88.95	3.419%	$91.9912	$91.99	$92.00	$92.00
Purchase #5	$246.46	13.824%	$280.5306	$280.53	$280.55	$280.50
Purchase #6	$124.76	11.669%	$139.3182	$139.32	$139.30	$139.30
Purchase #7	$22.48	12.506%	$25.2913	$25.29	$25.30	$25.30
7 purchase totals =	$789.05		$861.7622	$861.77	$861.75	$861.80