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	$249.86	8.272%	$270.5284	$270.53	$270.55	$270.50
Purchase #2	$73.32	8.228%	$79.3528	$79.35	$79.35	$79.40
Purchase #3	$96.27	13.376%	$109.1471	$109.15	$109.15	$109.10
Purchase #4	$195.57	11.755%	$218.5593	$218.56	$218.55	$218.60
Purchase #5	$86.82	3.616%	$89.9594	$89.96	$89.95	$90.00
Purchase #6	$149.70	13.336%	$169.664	$169.66	$169.65	$169.70
Purchase #7	$136.52	5.149%	$143.5494	$143.55	$143.55	$143.50
7 purchase totals =	$988.06		$1,080.7604	$1,080.76	$1,080.75	$1,080.80