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	$137.25	12.345%	$154.1935	$154.19	$154.20	$154.20
Purchase #2	$153.43	8.296%	$166.1586	$166.16	$166.15	$166.20
Purchase #3	$220.90	12.769%	$249.1067	$249.11	$249.10	$249.10
Purchase #4	$155.25	9.424%	$169.8808	$169.88	$169.90	$169.90
Purchase #5	$140.98	7.431%	$151.4562	$151.46	$151.45	$151.50
Purchase #6	$165.73	9.471%	$181.4263	$181.43	$181.45	$181.40
Purchase #7	$141.69	9.807%	$155.5855	$155.59	$155.60	$155.60
7 purchase totals =	$1,115.23		$1,227.8076	$1,227.82	$1,227.85	$1,227.90