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	$63.66	12.261%	$71.4654	$71.47	$71.45	$71.50
Purchase #2	$185.64	9.465%	$203.2108	$203.21	$203.20	$203.20
Purchase #3	$73.88	9.473%	$80.8787	$80.88	$80.90	$80.90
Purchase #4	$227.37	4.731%	$238.1269	$238.13	$238.15	$238.10
Purchase #5	$143.58	13.264%	$162.6245	$162.62	$162.60	$162.60
Purchase #6	$248.27	12.187%	$278.5267	$278.53	$278.55	$278.50
Purchase #7	$85.37	3.811%	$88.6235	$88.62	$88.60	$88.60
7 purchase totals =	$1,027.77		$1,123.4565	$1,123.46	$1,123.45	$1,123.40