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	$37.54	8.113%	$40.5856	$40.59	$40.60	$40.60
Purchase #2	$182.67	9.471%	$199.9707	$199.97	$199.95	$200.00
Purchase #3	$137.63	4.512%	$143.8399	$143.84	$143.85	$143.80
Purchase #4	$38.56	7.484%	$41.4458	$41.45	$41.45	$41.40
Purchase #5	$35.29	7.566%	$37.96	$37.96	$37.95	$38.00
Purchase #6	$240.90	7.356%	$258.6206	$258.62	$258.60	$258.60
Purchase #7	$80.27	7.167%	$86.023	$86.02	$86.00	$86.00
7 purchase totals =	$752.86		$808.4456	$808.45	$808.40	$808.40