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	$220.71	11.817%	$246.7913	$246.79	$246.80	$246.80
Purchase #2	$96.50	7.835%	$104.0608	$104.06	$104.05	$104.10
Purchase #3	$87.64	10.541%	$96.8781	$96.88	$96.90	$96.90
Purchase #4	$84.62	7.335%	$90.8269	$90.83	$90.85	$90.80
Purchase #5	$73.33	7.119%	$78.5504	$78.55	$78.55	$78.60
Purchase #6	$196.53	12.442%	$220.9823	$220.98	$221.00	$221.00
Purchase #7	$39.89	7.787%	$42.9962	$43.00	$43.00	$43.00
7 purchase totals =	$799.22		$881.0860	$881.09	$881.15	$881.20