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	$71.96	9.625%	$78.8862	$78.89	$78.90	$78.90
Purchase #2	$227.90	9.687%	$249.9767	$249.98	$250.00	$250.00
Purchase #3	$207.25	12.291%	$232.7231	$232.72	$232.70	$232.70
Purchase #4	$220.69	8.402%	$239.2324	$239.23	$239.25	$239.20
Purchase #5	$37.40	9.338%	$40.8924	$40.89	$40.90	$40.90
Purchase #6	$105.50	4.530%	$110.2792	$110.28	$110.30	$110.30
Purchase #7	$174.43	3.111%	$179.8565	$179.86	$179.85	$179.90
7 purchase totals =	$1,045.13		$1,131.8465	$1,131.85	$1,131.90	$1,131.90