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	$84.93	10.194%	$93.5878	$93.59	$93.60	$93.60
Purchase #2	$96.31	4.411%	$100.5582	$100.56	$100.55	$100.60
Purchase #3	$71.40	13.369%	$80.9455	$80.95	$80.95	$80.90
Purchase #4	$73.52	6.143%	$78.0363	$78.04	$78.05	$78.00
Purchase #5	$71.38	9.314%	$78.0283	$78.03	$78.05	$78.00
Purchase #6	$119.89	10.768%	$132.7998	$132.80	$132.80	$132.80
Purchase #7	$33.36	9.421%	$36.5028	$36.50	$36.50	$36.50
7 purchase totals =	$550.79		$600.4587	$600.47	$600.50	$600.40