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	$10.55	12.409%	$11.8591	$11.86	$11.85	$11.90
Purchase #2	$96.95	9.730%	$106.3832	$106.38	$106.40	$106.40
Purchase #3	$39.30	4.263%	$40.9754	$40.98	$41.00	$41.00
Purchase #4	$82.56	8.155%	$89.2928	$89.29	$89.30	$89.30
Purchase #5	$151.55	9.279%	$165.6123	$165.61	$165.60	$165.60
Purchase #6	$156.41	9.554%	$171.3534	$171.35	$171.35	$171.40
Purchase #7	$199.70	7.277%	$214.2322	$214.23	$214.25	$214.20
7 purchase totals =	$737.02		$799.7084	$799.70	$799.75	$799.80