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	$130.72	9.551%	$143.2051	$143.21	$143.20	$143.20
Purchase #2	$29.27	10.487%	$32.3395	$32.34	$32.35	$32.30
Purchase #3	$84.33	9.835%	$92.6239	$92.62	$92.60	$92.60
Purchase #4	$126.50	13.645%	$143.7609	$143.76	$143.75	$143.80
Purchase #5	$201.35	12.818%	$227.159	$227.16	$227.15	$227.20
Purchase #6	$162.30	3.616%	$168.1688	$168.17	$168.15	$168.20
Purchase #7	$99.86	8.488%	$108.3361	$108.34	$108.35	$108.30
7 purchase totals =	$834.33		$915.5933	$915.60	$915.55	$915.60