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	$232.76	7.244%	$249.6211	$249.62	$249.60	$249.60
Purchase #2	$132.93	6.841%	$142.0237	$142.02	$142.00	$142.00
Purchase #3	$205.64	9.523%	$225.2231	$225.22	$225.20	$225.20
Purchase #4	$73.68	6.729%	$78.6379	$78.64	$78.65	$78.60
Purchase #5	$121.50	8.148%	$131.3998	$131.40	$131.40	$131.40
Purchase #6	$233.97	3.791%	$242.8398	$242.84	$242.85	$242.80
Purchase #7	$57.61	3.439%	$59.5912	$59.59	$59.60	$59.60
7 purchase totals =	$1,058.09		$1,129.3366	$1,129.33	$1,129.30	$1,129.20