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	$237.64	13.655%	$270.0897	$270.09	$270.10	$270.10
Purchase #2	$74.96	4.590%	$78.4007	$78.40	$78.40	$78.40
Purchase #3	$116.98	6.423%	$124.4936	$124.49	$124.50	$124.50
Purchase #4	$86.84	13.768%	$98.7961	$98.80	$98.80	$98.80
Purchase #5	$226.37	6.253%	$240.5249	$240.52	$240.50	$240.50
Purchase #6	$125.86	11.653%	$140.5265	$140.53	$140.55	$140.50
Purchase #7	$63.25	7.325%	$67.8831	$67.88	$67.90	$67.90
7 purchase totals =	$931.90		$1,020.7146	$1,020.71	$1,020.75	$1,020.70