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	$167.42	6.751%	$178.7225	$178.72	$178.70	$178.70
Purchase #2	$188.72	9.365%	$206.3936	$206.39	$206.40	$206.40
Purchase #3	$240.72	6.813%	$257.1203	$257.12	$257.10	$257.10
Purchase #4	$174.79	12.411%	$196.4832	$196.48	$196.50	$196.50
Purchase #5	$38.98	9.429%	$42.6554	$42.66	$42.65	$42.70
Purchase #6	$212.43	5.473%	$224.0563	$224.06	$224.05	$224.10
Purchase #7	$53.56	3.404%	$55.3832	$55.38	$55.40	$55.40
7 purchase totals =	$1,076.62		$1,160.8145	$1,160.81	$1,160.80	$1,160.90