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	$53.86	3.698%	$55.8517	$55.85	$55.85	$55.90
Purchase #2	$196.99	12.409%	$221.4345	$221.43	$221.45	$221.40
Purchase #3	$168.26	9.124%	$183.612	$183.61	$183.60	$183.60
Purchase #4	$221.26	5.505%	$233.4404	$233.44	$233.45	$233.40
Purchase #5	$189.85	12.732%	$214.0217	$214.02	$214.00	$214.00
Purchase #6	$27.46	3.178%	$28.3327	$28.33	$28.35	$28.30
Purchase #7	$237.71	4.839%	$249.2128	$249.21	$249.20	$249.20
7 purchase totals =	$1,095.39		$1,185.9058	$1,185.89	$1,185.90	$1,185.80