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	$74.30	12.538%	$83.6157	$83.62	$83.60	$83.60
Purchase #2	$116.57	12.748%	$131.4303	$131.43	$131.45	$131.40
Purchase #3	$210.28	11.708%	$234.8996	$234.90	$234.90	$234.90
Purchase #4	$91.27	9.829%	$100.2409	$100.24	$100.25	$100.20
Purchase #5	$202.48	12.395%	$227.5774	$227.58	$227.60	$227.60
Purchase #6	$210.41	4.500%	$219.8785	$219.88	$219.90	$219.90
Purchase #7	$241.82	9.146%	$263.9369	$263.94	$263.95	$263.90
7 purchase totals =	$1,147.13		$1,261.5793	$1,261.59	$1,261.65	$1,261.50