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	$96.74	8.703%	$105.1593	$105.16	$105.15	$105.20
Purchase #2	$143.71	3.598%	$148.8807	$148.88	$148.90	$148.90
Purchase #3	$39.61	7.351%	$42.5217	$42.52	$42.50	$42.50
Purchase #4	$94.90	9.807%	$104.2068	$104.21	$104.20	$104.20
Purchase #5	$125.33	7.835%	$135.1496	$135.15	$135.15	$135.10
Purchase #6	$127.61	12.333%	$143.3481	$143.35	$143.35	$143.30
Purchase #7	$98.47	13.633%	$111.8944	$111.89	$111.90	$111.90
7 purchase totals =	$726.37		$791.1606	$791.16	$791.15	$791.10