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	$75.80	7.498%	$81.4835	$81.48	$81.50	$81.50
Purchase #2	$80.90	3.694%	$83.8884	$83.89	$83.90	$83.90
Purchase #3	$130.76	8.849%	$142.331	$142.33	$142.35	$142.30
Purchase #4	$240.55	6.384%	$255.9067	$255.91	$255.90	$255.90
Purchase #5	$42.37	9.673%	$46.4685	$46.47	$46.45	$46.50
Purchase #6	$123.87	5.453%	$130.6246	$130.62	$130.60	$130.60
Purchase #7	$157.64	12.656%	$177.5909	$177.59	$177.60	$177.60
7 purchase totals =	$851.89		$918.2936	$918.29	$918.30	$918.30