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	$100.77	8.219%	$109.0523	$109.05	$109.05	$109.10
Purchase #2	$139.85	7.769%	$150.7149	$150.71	$150.70	$150.70
Purchase #3	$113.37	9.217%	$123.8193	$123.82	$123.80	$123.80
Purchase #4	$142.75	9.712%	$156.6139	$156.61	$156.60	$156.60
Purchase #5	$79.72	8.793%	$86.7298	$86.73	$86.75	$86.70
Purchase #6	$224.54	9.609%	$246.116	$246.12	$246.10	$246.10
Purchase #7	$48.36	4.376%	$50.4762	$50.48	$50.50	$50.50
7 purchase totals =	$849.36		$923.5224	$923.52	$923.50	$923.50