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	$38.71	4.331%	$40.3865	$40.39	$40.40	$40.40
Purchase #2	$130.87	11.376%	$145.7578	$145.76	$145.75	$145.80
Purchase #3	$171.40	6.387%	$182.3473	$182.35	$182.35	$182.30
Purchase #4	$178.98	6.824%	$191.1936	$191.19	$191.20	$191.20
Purchase #5	$161.73	6.285%	$171.8947	$171.89	$171.90	$171.90
Purchase #6	$177.91	12.202%	$199.6186	$199.62	$199.60	$199.60
Purchase #7	$40.26	5.324%	$42.4034	$42.40	$42.40	$42.40
7 purchase totals =	$899.86		$973.6019	$973.60	$973.60	$973.60