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	$39.91	7.153%	$42.7648	$42.76	$42.75	$42.80
Purchase #2	$6.27	6.340%	$6.6675	$6.67	$6.65	$6.70
Purchase #3	$106.51	9.251%	$116.3632	$116.36	$116.35	$116.40
Purchase #4	$9.62	9.718%	$10.5549	$10.55	$10.55	$10.60
Purchase #5	$227.32	9.817%	$249.636	$249.64	$249.65	$249.60
Purchase #6	$64.96	4.545%	$67.9124	$67.91	$67.90	$67.90
Purchase #7	$225.58	13.270%	$255.5145	$255.51	$255.50	$255.50
7 purchase totals =	$680.17		$749.4133	$749.40	$749.35	$749.50