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	$71.97	8.729%	$78.2523	$78.25	$78.25	$78.30
Purchase #2	$53.58	3.199%	$55.294	$55.29	$55.30	$55.30
Purchase #3	$192.87	13.705%	$219.3028	$219.30	$219.30	$219.30
Purchase #4	$237.93	8.625%	$258.4515	$258.45	$258.45	$258.50
Purchase #5	$179.68	13.175%	$203.3528	$203.35	$203.35	$203.40
Purchase #6	$71.64	12.169%	$80.3579	$80.36	$80.35	$80.40
Purchase #7	$80.64	3.512%	$83.4721	$83.47	$83.45	$83.50
7 purchase totals =	$888.31		$978.4834	$978.47	$978.45	$978.70