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	$59.27	13.217%	$67.1037	$67.10	$67.10	$67.10
Purchase #2	$240.84	7.448%	$258.7778	$258.78	$258.80	$258.80
Purchase #3	$50.44	12.673%	$56.8323	$56.83	$56.85	$56.80
Purchase #4	$25.29	9.270%	$27.6344	$27.63	$27.65	$27.60
Purchase #5	$37.57	7.659%	$40.4475	$40.45	$40.45	$40.40
Purchase #6	$46.69	9.760%	$51.2469	$51.25	$51.25	$51.20
Purchase #7	$96.82	12.137%	$108.571	$108.57	$108.55	$108.60
7 purchase totals =	$556.92		$610.6136	$610.61	$610.65	$610.50