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	$25.95	10.793%	$28.7508	$28.75	$28.75	$28.80
Purchase #2	$65.82	10.240%	$72.56	$72.56	$72.55	$72.60
Purchase #3	$101.94	13.336%	$115.5347	$115.53	$115.55	$115.50
Purchase #4	$248.25	12.678%	$279.7231	$279.72	$279.70	$279.70
Purchase #5	$165.96	8.663%	$180.3371	$180.34	$180.35	$180.30
Purchase #6	$216.65	3.275%	$223.7453	$223.75	$223.75	$223.70
Purchase #7	$216.46	10.391%	$238.9524	$238.95	$238.95	$239.00
7 purchase totals =	$1,041.03		$1,139.6034	$1,139.60	$1,139.60	$1,139.60