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	$71.81	9.853%	$78.8854	$78.89	$78.90	$78.90
Purchase #2	$93.46	3.221%	$96.4703	$96.47	$96.45	$96.50
Purchase #3	$112.62	13.483%	$127.8046	$127.80	$127.80	$127.80
Purchase #4	$167.36	5.280%	$176.1966	$176.20	$176.20	$176.20
Purchase #5	$172.39	9.809%	$189.2997	$189.30	$189.30	$189.30
Purchase #6	$104.76	6.793%	$111.8763	$111.88	$111.90	$111.90
Purchase #7	$196.29	4.213%	$204.5597	$204.56	$204.55	$204.60
7 purchase totals =	$918.69		$985.0926	$985.10	$985.10	$985.20