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	$49.35	9.337%	$53.9578	$53.96	$53.95	$54.00
Purchase #2	$139.28	3.773%	$144.535	$144.54	$144.55	$144.50
Purchase #3	$235.44	9.110%	$256.8886	$256.89	$256.90	$256.90
Purchase #4	$78.31	8.771%	$85.1786	$85.18	$85.20	$85.20
Purchase #5	$86.95	10.295%	$95.9015	$95.90	$95.90	$95.90
Purchase #6	$116.95	3.260%	$120.7626	$120.76	$120.75	$120.80
Purchase #7	$156.27	11.410%	$174.1004	$174.10	$174.10	$174.10
7 purchase totals =	$862.55		$931.3245	$931.33	$931.35	$931.40