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	$192.71	13.841%	$219.383	$219.38	$219.40	$219.40
Purchase #2	$101.58	11.131%	$112.8869	$112.89	$112.90	$112.90
Purchase #3	$174.90	12.404%	$196.5946	$196.59	$196.60	$196.60
Purchase #4	$174.93	10.386%	$193.0982	$193.10	$193.10	$193.10
Purchase #5	$227.53	3.387%	$235.2364	$235.24	$235.25	$235.20
Purchase #6	$181.93	5.338%	$191.6414	$191.64	$191.65	$191.60
Purchase #7	$138.82	8.298%	$150.3393	$150.34	$150.35	$150.30
7 purchase totals =	$1,192.40		$1,299.1798	$1,299.18	$1,299.25	$1,299.10