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	$218.29	6.118%	$231.645	$231.65	$231.65	$231.60
Purchase #2	$206.49	7.328%	$221.6216	$221.62	$221.60	$221.60
Purchase #3	$53.66	10.346%	$59.2117	$59.21	$59.20	$59.20
Purchase #4	$5.76	3.563%	$5.9652	$5.97	$5.95	$6.00
Purchase #5	$139.96	5.151%	$147.1693	$147.17	$147.15	$147.20
Purchase #6	$111.89	10.626%	$123.7794	$123.78	$123.80	$123.80
Purchase #7	$133.70	6.440%	$142.3103	$142.31	$142.30	$142.30
7 purchase totals =	$869.75		$931.7025	$931.71	$931.65	$931.70