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	$171.96	3.844%	$178.5701	$178.57	$178.55	$178.60
Purchase #2	$200.25	13.850%	$227.9846	$227.98	$228.00	$228.00
Purchase #3	$182.94	6.765%	$195.3159	$195.32	$195.30	$195.30
Purchase #4	$151.37	5.377%	$159.5092	$159.51	$159.50	$159.50
Purchase #5	$78.79	10.837%	$87.3285	$87.33	$87.35	$87.30
Purchase #6	$149.37	11.188%	$166.0815	$166.08	$166.10	$166.10
Purchase #7	$68.98	3.435%	$71.3495	$71.35	$71.35	$71.30
7 purchase totals =	$1,003.66		$1,086.1393	$1,086.14	$1,086.15	$1,086.10