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	$64.34	4.678%	$67.3498	$67.35	$67.35	$67.30
Purchase #2	$38.31	5.226%	$40.3121	$40.31	$40.30	$40.30
Purchase #3	$131.99	9.609%	$144.6729	$144.67	$144.65	$144.70
Purchase #4	$235.76	5.866%	$249.5897	$249.59	$249.60	$249.60
Purchase #5	$168.82	9.558%	$184.9558	$184.96	$184.95	$185.00
Purchase #6	$86.69	4.427%	$90.5278	$90.53	$90.55	$90.50
Purchase #7	$213.45	12.599%	$240.3426	$240.34	$240.35	$240.30
7 purchase totals =	$939.36		$1,017.7507	$1,017.75	$1,017.75	$1,017.70