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	$113.91	6.561%	$121.3836	$121.38	$121.40	$121.40
Purchase #2	$147.42	7.409%	$158.3423	$158.34	$158.35	$158.30
Purchase #3	$182.95	7.538%	$196.7408	$196.74	$196.75	$196.70
Purchase #4	$182.94	7.479%	$196.6221	$196.62	$196.60	$196.60
Purchase #5	$41.88	4.243%	$43.657	$43.66	$43.65	$43.70
Purchase #6	$222.96	10.223%	$245.7532	$245.75	$245.75	$245.80
Purchase #7	$78.46	10.677%	$86.8372	$86.84	$86.85	$86.80
7 purchase totals =	$970.52		$1,049.3362	$1,049.33	$1,049.35	$1,049.30