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	$25.63	9.297%	$28.0128	$28.01	$28.00	$28.00
Purchase #2	$180.40	6.123%	$191.4459	$191.45	$191.45	$191.40
Purchase #3	$103.31	5.591%	$109.0861	$109.09	$109.10	$109.10
Purchase #4	$72.33	11.403%	$80.5778	$80.58	$80.60	$80.60
Purchase #5	$187.99	4.702%	$196.8293	$196.83	$196.85	$196.80
Purchase #6	$193.56	12.630%	$218.0066	$218.01	$218.00	$218.00
Purchase #7	$109.69	8.343%	$118.8414	$118.84	$118.85	$118.80
7 purchase totals =	$872.91		$942.7999	$942.81	$942.85	$942.70