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	$215.47	13.816%	$245.2393	$245.24	$245.25	$245.20
Purchase #2	$102.81	12.108%	$115.2582	$115.26	$115.25	$115.30
Purchase #3	$62.39	12.749%	$70.3441	$70.34	$70.35	$70.30
Purchase #4	$38.82	9.178%	$42.3829	$42.38	$42.40	$42.40
Purchase #5	$204.32	8.805%	$222.3104	$222.31	$222.30	$222.30
Purchase #6	$5.34	9.470%	$5.8457	$5.85	$5.85	$5.80
Purchase #7	$156.51	6.669%	$166.9477	$166.95	$166.95	$166.90
7 purchase totals =	$785.66		$868.3283	$868.33	$868.35	$868.20