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	$212.53	12.326%	$238.7264	$238.73	$238.75	$238.70
Purchase #2	$100.74	11.639%	$112.4651	$112.47	$112.45	$112.50
Purchase #3	$31.89	5.802%	$33.7403	$33.74	$33.75	$33.70
Purchase #4	$12.88	11.683%	$14.3848	$14.38	$14.40	$14.40
Purchase #5	$97.39	9.436%	$106.5797	$106.58	$106.60	$106.60
Purchase #6	$123.31	12.530%	$138.7607	$138.76	$138.75	$138.80
Purchase #7	$19.71	5.620%	$20.8177	$20.82	$20.80	$20.80
7 purchase totals =	$598.45		$665.4747	$665.48	$665.50	$665.50