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	$75.44	9.801%	$82.8339	$82.83	$82.85	$82.80
Purchase #2	$124.28	12.556%	$139.8846	$139.88	$139.90	$139.90
Purchase #3	$160.69	7.392%	$172.5682	$172.57	$172.55	$172.60
Purchase #4	$93.47	3.311%	$96.5648	$96.56	$96.55	$96.60
Purchase #5	$21.50	4.646%	$22.4989	$22.50	$22.50	$22.50
Purchase #6	$225.68	6.504%	$240.3582	$240.36	$240.35	$240.40
Purchase #7	$54.85	13.261%	$62.1237	$62.12	$62.10	$62.10
7 purchase totals =	$755.91		$816.8323	$816.82	$816.80	$816.90